1 48 class: unit 4: it’s getting hot in here · 04.02.2020 · 7. use a utility clamp to obtain...

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Class:

Unit 4: It’s Getting Hot in Here Topics/ Daily Outline: Day A B Content: CW: HW: TEXT:

1 2/3 1/31 Thermodynamic systems 1, 2 1 17.1 2 2/5 2/4 Heat and temperature 3 -- 17.1

3 2/7 2/6 Heating and cooling curves 4 2 17.3

4 2/11 2/10 Heat during phase changes 5 -- 17.3 5 2/13 2/12 Phase changes 6 3 17.3

6 2/18 2/14 Specific heat, Quiz 1 7 -- 17.1

7 2/20 2/19 Endothermic and exothermic processes 8, 9 4 17.1, 17.2

8 2/24 2/21 Heat of solution 10 -- 17.2 9 2/26 2/25 Heat of neutralization 11 -- 17.2

10 2/28 2/27 Bond enthalpies, Hess’ law 12, 13 5 17.4

11 3/3 3/2 Rate of reaction, Catalysts 14 6 18.1 12 3/5 3/4 Flex Day/ Review -- -- --

13 3/9 3/6 Project Presentations -- -- --

14 3/12 3/11 Unit Test -- -- --

For tutorials and additional resources: www.leffellabs.com If you are absent, please use this sheet to determine what you missed and collect the materials from the make-up work bins up front. Get help from a friend, the link above, or the instructor.

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Important Due Dates:

• Freezing Point of Lauric Acid Lab Write Up, 2/13 (A) and 2/14 (B)

• Energy Transformation Project Proposal, 2/20 (A) and 2/21 (B)

• Journals, 3/5 (A) and 3/4 (B)

• Heat of Neutralization Lab Report, 3/3 (A) and 3/4 (B)

• Energy Transformation Project Presentation, 3/9 (A) and 3/6 (B)

• Poster Project, 3/30 (A) and 3/31 (B)

• Threaded Ions Project, 4/16 (A) and 4/17 (B)

Homework:

HW 1: Heat Calculations HW 2: Heating and Cooling Curves HW 3: Calorimetry and Specific Heat HW 4: Enthalpy Diagrams HW 5 Practice using Hess’ Law and Bond Enthalpies HW 6: Review for Unit Test

Quizzes:

Quiz 1: CW 1 to CW 6

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Drills

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CW 1: Thermodynamic Systems

Thermochemistry is the study of energy changes that occur during chemical reactions and changes in state, generally involving either the absorption or the release of heat. In studying energy changes, you can define a system as the part of the universe on which you focus your attention. Everything else in the universe makes up the surroundings. Together, the system and its surroundings make up the universe. A major goal of thermochemistry is to examine the flow of heat between the system and its surroundings.

1. For each of the following, define the system and the surroundings.

System: Surroundings:

System: Surroundings:

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2. Define the following, using the provided notes: System Definition Example

Open System

Closed System

Isolated System

3. Which type of thermodynamic system is…?

a. An ocean?

b. An aquarium?

c. A pizza delivery bag?

d. A greenhouse?

4. An isolated system has an initial temperature of 30°C. It is then placed on top of a Bunsen burner for an hour. What is the final temperature?

Journal Write 1 Why do we want an isolated system when studying heat? Is possible to construct an isolated system? Explain.

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CW 2: Heat Exchange

The Mitten and the Vessel 1. Watch the demonstration as your instructor places a thermometer inside of a mitten.

Record the initial and final temperatures inside the mitten.

Data Table - Mitten

Initial Temperature

Final Temperature

∆T (change in temperature)

2. You will be given 10 minutes to design and build a vessel that can keep a sample of hot

water at the same temperature for as long as possible, using the provided materials. Once your device is built, obtain hot water and a thermometer. You will measure the initial temperature and the final temperature after 3 minutes have past.

Data Table - Vessel

Initial Temperature (time = 0 min)

Final Temperature (time = 3 min)

∆T (change in temperature)

3. Based on your data, draw a diagram showing the heat flow (in/ out) for each system.

Consider how to represent the following: amount of heat loss, ate of heat loss, if the system is the same temperature (or a different temperature) from the surroundings.

Mitten

Vessel

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Heat vs. Temperature Heat is the total energy of molecular motion in a substance. Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object. Temperature is a measure of the average energy of molecular motion in a substance. Temperature does not depend on the size or type of object.

4. Consider a coffee cup of boiling water and a bathtub of boiling water. a. What is the temperature of both samples of water?

b. Which sample has more heat energy?

c. Which sample would you rather have dumped over your head? Why?

5. Which contains more heat: a burning match or an iceberg? Why?

Journal Write 2 Explain the difference between temperature and heat using the match and iceberg example.

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CW 3: Heat and Temperature

Directions 1. Read ALL the directions so you don’t waste your time. 2. Go to http://mw.concord.org/modeler/. Scroll and click on “Heat & Temperature.” 3. Read the statement or question at the top of each page. Consider this information as

you complete each page, making sure to READ the words on the page, including directions for how to run each molecular model.

4. As you READ, define/ explain the key phrases below. 5. Answer the questions by typing into the windows and using the snapshot button. 6. Once get to page 9, ask your instructor for the summary assessment. You will complete

this for a grade. You are welcome to reference the activity as you complete this. 7. If you wish to save your work:

a. Click on the “Create a report of my work” button. b. When the window pops up, click “Print without login.” c. Type in your name and class period. d. Once the report opens, click on “Print.” e. Under Printer Name, choose “Inspiration 9 PDF Driver,” then click “OK.” f. When the next window pops up, click “OK.” g. When the PDF opens, click on “File” then “Save As…” and save the document.

Key Phrases • Absolute zero (Page 1)

• Kinetic energy (Page 2)

• Average kinetic energy (Page 3)

• Thermal equilibrium (Page 6)

• Potential energy (Page 8)

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CW 4: Finding the Freezing Point of Lauric Acid

1. Is this a heating curve or a cooling curve? Explain.

2. Determine the following for the substance A: a. Freezing Point

b. Melting Point

c. Boiling Point

d. Condensation Point

3. Explain how the data on the graph was collected.

Temperature vs. Time for Substance A

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Procedure 1. On a separate sheet of paper, paraphrase the procedure, underlining all materials.

Create a data table that includes observations, sources of error, average freezing point (as described in step 12).

2. Obtain and wear goggles. 3. Logon to a laptop and open LoggerPro, a program on the desktop. 4. Connect the Temperature Probe to the computer interface. 5. Prepare the computer for data collection by opening the file “15 Freezing Pt

Depression” from the Chemistry with Vernier folder. 6. Add about 300 mL of room temperature tap water a 400 mL beaker. Place the beaker on

the base of the ring stand. 7. Use a utility clamp to obtain a test tube containing hot melted lauric acid. Attach the

utility clamp to the ring stand so that it is above the water. 8. Insert the Temperature Probe into the hot lauric acid. Allow 30 seconds for the probe to

warm up to the temperature of its surroundings and give correct temperature readings. Press collect to begin collecting data.

9. Lower the test tube (with the temperature probe inside) .into the water bath. Make sure the water level outside the test tube is higher than the lauric acid level inside the test tube. If the lauric acid is not above 50°C, obtain another lauric acid sample and begin again.

10. With a very slight up and down motion of the Temperature Probe, continuously stir the lauric acid during the cooling. Hold the top of the probe and not its wire.

11. Continue with the experiment until data collection has stopped after 10 minutes. 12. To determine the freezing temperature of pure lauric acid, you need to determine the

mean (or average) temperature in the portion of graph with nearly constant temperature. Move the mouse pointer to the beginning of the graph’s flat part. Press the mouse button and hold it down as you drag across the flat part of the curve, selecting only the points in the plateau. Click the Statistics button, . The mean temperature value for the selected data is listed in the statistics box on the graph. Record this value as the freezing temperature of lauric acid. Close the statistics box.

13. Use the hot water bath to melt the probe out of the solid lauric acid. Do not attempt to pull the probe out—this might damage it. Carefully wipe any excess lauric acid liquid from the probe with a paper towel. Return the test tube containing lauric acid and utility clamp to Ms. Leffel.

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Lab Write Up To complete this lab, you will complete a lab write up, using this sheet to guide you. Your final lab write up should be typed and submitted in class. The following sections should be completed, in order, as they appear below.

Data Organize ALL data into a neat data table. You will need in depth observations. Include:

• Experimental setup and procedural notes

• General observations and possible sources of error

• Average freezing point as determined by step 12 in the given procedure

• Printed (computer) copy of the cooling curve graph – attach this to your printed report.

Conclusion Questions Answer the following questions using complete sentences. You should use at least 5 sentences for each question. For calculations, show all work, including units.

1. The actual freezing point of lauric acid is 43.2°C. Determine the percent error of your measurement of the freezing point.

% 𝑒𝑟𝑟𝑜𝑟 = |𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 − 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑣𝑎𝑙𝑢𝑒|

𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒× 100%

2. Describe a possible source of error and specify how it effected your measurement of the freezing point. This should not be a general discussion of errors, rather, if you freezing point is too high (or too low), what specific errors could have caused this?

3. Explain the features of the graph in terms of energy changes that occur as the lauric acid cools down and freezes (what is happening during each segment of the graph)? Make sure to discuss where kinetic energy and potential energy is constant and where they are changing for each segment of the graph. You may wish to review CW 3, CW 6, and HW 2 to answer this question

4. What effect would increasing the amount of lauric acid present in the test tube have on the freezing point and the shape/ features of the graph?

Rubric Data table /5

Question 1 /5

Question 2 /5 Question 3 /5

Question 4 /5

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CW 5: Calculating Heat during Phase Changes

As you already know, adding or removing heat energy from a substance may lead to a phase change. For example, heating ice will cause it to melt into liquid water.

1. Define the following terms. a. Molar heat of fusion

b. Molar heat of solidification

c. Molar heat of vaporization

d. Molar heat of condensation

2. Label and explain the diagram below.

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Only the heats of fusion and vaporization are used to calculate enthalpy. Some logic can be applied to determine if the phase change is endothermic or exothermic based on the direction of heat flow. All values are found at the normal freezing and vaporization points for the substance.

3. How many grams of ice at 0°C will melt if 2.25 kJ of heat are added?

4. How many kilojoules of heat are required to melt a 50.0 gram popsicle at 0°C? Assume that the popsicle has the same molar mass and heat of fusion as water.

5. How much heat is absorbed when 63.7 g H2O(l) is converted to H2O(g) at 100°C?

6. How many kilojoules of heat are absorbed when 0.46 g of chloroethane (C2H5Cl) is vaporized at its normal boiling point? The ∆Hvap of chloroethane is 24.7 kJ/mol.

Journal Write 3 How do intermolecular forces affect the values for ∆Hfus and ∆Hvap? Compare the ∆Hfus for two substances: one with strong intermolecular forces, and one with weak intermolecular forces.

Substance ∆Hfus (kJ/mol) ∆Hvap (kJ/mol) Ammonia (NH3) 5.66 23.3

Ethanol (C2H6O) 4.93 38.6 Hydrogen (H2) 0.12 0.90

Methanol (CH4O) 3.22 35.2 Oxygen (O2) 0.44 6.82

Water (H2O) 6.01 40.7

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CW 6: Phase Change

Directions 1. Read ALL the directions so you don’t waste your time. 2. Go to http://mw.concord.org/modeler/. Scroll and click on “Phase Change.” 3. Read the statement or question at the top of each page. Consider this information as

you complete each page, making sure to READ the words on the page, including directions for how to run each molecular model.

4. As you READ, define/ explain the key phrases below. 5. Answer the questions by typing into the windows and using the snapshot button. 6. Once get to page 9, ask your instructor for the summary assessment. You will complete

this for a grade. You are welcome to reference the activity as you complete this. 7. If you wish to save your work:

a. Click on the “Create a report of my work” button. b. When the window pops up, click “Print without login.” c. Type in your name and class period. d. Once the report opens, click on “Print.” e. Under Printer Name, choose “Inspiration 9 PDF Driver,” then click “OK.” f. When the next window pops up, click “OK.” g. When the PDF opens, click on “File” then “Save As…” and save the document.

Key Phrases • State of matter (Page 5)

• Attractions between particles (Page 5)

• Kinetic energy (Page 6)

• Phase change (Page 7)

• Evaporative cooling (Page 8)

• Costs energy to pull two attracting molecules apart (Page 8)

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CW 7: Specific Heat of a Metal

Objective Calculate the specific heat of a metal to identify the metal.

Materials • Laptop with LoggerPro

• Temperature probe

• Hot plate

• Test tube

• Test tube holder

• Unknown metal sample

• Styrofoam cup

• 250 mL beaker (2)

• Balance

• Distilled water

• Thermometer

• Goggles

Procedure 1. Obtain and wear goggles. 2. Measure and record the mass of an empty, dry test tube. Gently place a metal sample

inside the test tube. Measure and record the mass of the test tube and metal sample. 3. Using the test tube holder, place the test tube with the metal sample into the beaker of

boiling water. Ensure all metal is below the surface of the water, adding more water if necessary.

4. Measure and record the mass of an empty Styrofoam cup. Half fill the Styrofoam cup with distilled water. Measure and record the mass of the cup and distilled water.

5. Connect the probe to the computer. Open LoggerPro. Prepare the program for data collection by opening the file “04 Heat of Fusion” from the Chemistry with Vernier folder.

6. Ensure that the metal has been in the boiling water for at least 5 minutes. Use a thermometer to determine the boiling temperature of the water.

7. Place the temperature probe into the distilled water in the Styrofoam cup. Click

to begin data collection. Wait until the temperature remains constant. This will be the initial temperature, T1, of the water.

8. Once T1 has been reached, use a test tube holder to pour the hot metal from the test tube into the Styrofoam cup. Stir the water with the temperature probe until the temperature stops rising. Record this maximum temperature as T2. Click to finish collecting data.

9. You can confirm your data by clicking the statistics button, . The maximum temperature (T2) and the beginning (minimum) temperature (T1) are listed in the floating box on the graph.

10. Dry and neatly return all materials to the bin.

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Data Table

Metal identification letter

Mass of metal

Mass of empty Styrofoam cup

Mass of Styrofoam cup and distilled water

Starting temperature of water (T1 of water)

Starting temperature of metal (T1 of metal)

Final temperature of system (T2 of metal and water)

Analysis Questions 1. Find the change in temperature of the water (ΔT = T2 – T1).

2. Calculate the mass of the water

3. Calculate the heat gained by the water (same as the heat lost by the metal).

4. Find the change in temperature of the metal (ΔT = T2 – T1).

5. Calculate the mass of the metal.

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6. Using your answers to question 3, 4, and 5, find the specific heat of the unknown metal.

7. Obtain the actual value for the specific heat of your metal from your instructor.

8. Calculate the percentage error.

% 𝑒𝑟𝑟𝑜𝑟 = |𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 − 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑣𝑎𝑙𝑢𝑒|

𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒× 100%

9. List possible sources of error for this experimental and how they affected your data and calculation of specific heat.

Journal Write 4 Why did you have to use 𝑞 = 𝑚 ∙ 𝐶 ∙ ∆𝑇 twice during your calculations of the specific heat of the metal?

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CW 8: Endothermic and Exothermic Processes

Introduction Many chemical reactions give off energy. Chemical reactions that release energy are called exothermic reactions. Conversely, some chemical reactions absorb energy and are called endothermic reactions. You will study one endothermic and one exothermic reaction in this experiment. In part I, you will study the reaction between citric acid and baking soda. (1) H3C6H5O7(aq) + 3 NaHCO3(s) → 3 CO2(g) + 3 H2O(l) + Na3C6H5O7(aq)

In part II, you will study the reaction between magnesium metal and hydrochloric acid. (2) Mg + 2 HCl → H2(g) + MgCl2(aq)

Data Table Measurement Part I Part II

Final Temperature, T2 °C °C

Initial Temperature, T1 °C °C

Temperature Change, ΔT °C °C

Observations

Questions 1. What was the system in reaction 1? (Refer to CW 1 if needed to define system.)

2. What was the system in reaction 2?

3. What were the surroundings in both reactions? (Refer to CW 1 if needed.)

4. Calculate the temperature change, ΔT, for each reaction by subtracting the initial temperature from the final temperature (ΔT = T2 – T1). Fill it in the data table.

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5. Make a claim about which reaction is exothermic. Provide evidence.

6. Which reaction has a negative ΔT value? Is the reaction endothermic or exothermic? Explain.

7. For each reaction, describe three ways you could tell a reaction was taking place.

Journal Write 5 For each of the following processes, indicate if it is a physical change or a chemical change and explain if it is endothermic or exothermic.

• Ice melting

• Paper burning

• Make up your own example

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CW 9: Thermochemical Equations

What is Enthalpy? Enthalpy (H) is the amount of heat content used or released in a system at constant pressure, usually expressed as the change in enthalpy (ΔH) for the system. The value of ΔH of a reaction can be determined by measuring the heat flow of the reaction at constant pressure. For our purposes, heat and enthalpy change are interchangeable terms because we perform all reactions under the constant pressure of the atmosphere. In other words, q = ΔH. In a chemical reaction, the enthalpy change for the reaction can be written as either a reactant or a product, as below. In this reaction, heat is a product, meaning that heat is being released and the reaction is exothermic.

CaO(s) + H2O(l) → Ca(OH)2(s) + 65.2 kJ

Heats of Reaction The heat of reaction is the enthalpy change for the chemical reaction exactly as it is written, including the physical state of the reactants and products. The heat of reaction comes in many forms, such as the heat of neutralization or heat of combustion, but all measure the same quantity. You will usually see heats of reaction reported as ΔH.

1. For each of the following, determine if the reaction is endothermic or exothermic, writing ΔH with the correct sign.

a. Mn(s) + 2 HCl(aq) → MnCl2(aq) + H2(g) + 221 kJ Endo or Exo?

(circle one) ΔH =

b. 2 N2O5 (g) + 110 kJ → 4NO2(g) + O2(g)

Endo or Exo? (circle one)

ΔH =

c. P4O10(g) + 6H2O(l) → 4 H3PO4(aq) + 424 kJ

Endo or Exo? (circle one)

ΔH =

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Chemistry problems involving enthalpy changes are like stoichiometry problems. The amount of heat released or absorbed depends on the number of moles of the reactants involved.

2. When 2 mol of solid magnesium combines with 1 mol of oxygen gas, 2 mol of solid magnesium oxide is formed and 1204 kJ of heat is released. Write the thermochemical equation for this combustion reaction, then complete the enthalpy diagram.

3. Calculate the amount of heat (in kJ) required to decompose 2.24 mol NaHCO3(s), then complete the enthalpy diagram.

2 NaHCO3(s) + 85 kJ → Na2CO3(s) + H2O(l) + CO2(g)

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When ethanol burns, it reacts with O2(g) to produce CO2(g) and H2O(l). C2H6O(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(l) ΔH = -1368 kJ

4. Complete the enthalpy diagram for the reaction above.

5. How much heat is released when 12.5 g of ethanol reacts?

6. If 2063 kJ of energy are produced, what how many liters of O2 reacted?

Journal Write 6 Write your own thermochemistry problem based on the equation below using the provided post it note. After writing the problem on the post it, trade your post it with another student, and solve the problem in your journal. Tape the post it inside as well. Use questions 5 and 6 as models.

C(s) + 2 S(s) → CS2(l) ΔH = 89.3 kJ

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CW 10: Heat of Solution

Cold Pack Demonstration 1. Examine the deconstructed cold pack. List what you see.

2. Explain what happens when you “activate” a cold pack. What process is occurring inside the pack?

3. Based on the demonstration… a. Did the temperature of the solution increase or decrease?

b. Is the dissolving process endothermic or exothermic?

4. In this activity, you will add four different ionic salts to water, measuring the temperature change using a thermometer. Your goal will be to determine the heat released or absorbed per mole of each ionic salt (ΔHsoln), allowing you to rank the solutions from most to least endothermic.

a. What is the dependent variable (what are you trying to measure/ find)?

b. What is the independent variable (what is different for each trial)?

Materials • KCl (s)

• CaCl2 (s)

• NaCO3 (s)

• NaHCO3 (s)

• Styrofoam cup

• Scale

• Thermometer

• Pipette

• Scoopulas/ plastic spoons

• 100 mL beaker

• Distilled water

• 10 mL graduated cylinder

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Procedure 1. You will be assigned one solid. Label a clean, dry Styrofoam cup as your solid. 2. Place the cup onto a balance. Mass out about 2 grams of the solid into the cup. Record

the actual mass in the data table. 3. Obtain a beaker with about 30 mL of distilled water at room temperature. Using the

thermometer, record the initial temperature of the water, T1. 4. Using the pipette and graduated cylinder, measure out 10 mL of distilled water. 5. Place the thermometer into the cup. Pour the distilled water into the cup and swirl the

cup. Watch the thermometer. When the temperature stops changing, record the maximum temperature as T2.

6. Wipe the thermometer clean with a wet paper towel, rinse and dry your cup. 7. Share data with your classmates for the other solids.

Data Analysis 1. Determine the change in temperature for each solution (ΔT = T2 – T1). 2. Determine the heat transfer for the dissolving of each ionic salt. You may assume that

10 mL of water has a mass of 10 grams. The specific heat of water is 4.18 J/g°C 3. Determine the number of moles for each ionic salt using the grams you record in the

data table. The molar mass of each ionic salt is provided in the data table. 4. Using the heat and the moles you calculated, determine the ΔHsoln (ΔH/mol).

Data Table Salt KCl CaCl2 Na2CO3 NaHCO3

Target Mass (g)

Actual Mass (g)

T1

(°C)

T2 (°C)

ΔT

Molar Mass (g/mole)

74.55 110.98 83.00 84.01

Moles

Heat Transferred (q = ΔH=mcΔT)

ΔHsoln (ΔH/moles)

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Conclusion 5. Consider the diagram below, which shows how a solution is formed.

Step 1 Step 2

a. Is this process endothermic or exothermic?

b. How does the size of the arrows relate to the change in temperature of the

solution?

c. Which solutions does this picture apply to?

6. Consider the diagram below, which shows how a solution is formed.

Step 1 Step 2

a. Is this process endothermic or exothermic?

b. How does the size of the arrows relate to the change in temperature of the

solution?

c. Which solutions does this picture apply to?

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CW 11: Heat of Neutralization

Exp. HCl NaOH Total Mass

1 100.0 mL 1.00 M 100.0 mL 1.00 M 200.0 g 2 100.0 mL 2.00 M 100.0 mL 2.00 M 200.0 g

3 50.0 mL 1.00 M 50.0 mL 1.00 M 100.0 g

1. Use molarity to calculate the moles of HCl that are reacting for each reaction. Reaction 1 Reaction 2 Reaction 3

2. Using moles of HCl and the equation below, how much heat will each produce? HCl + NaOH → NaCl + H2O ∆H = –57 kJ/mol

Reaction 1 Reaction 2 Reaction 3

3. Solve for the temperature change brought about this amount of heat.

∆𝑇 =𝑞

𝑚𝑐 𝑐 = 0.00418

𝑘𝐽𝑔℃⁄ m = mass of solution

Reaction 1 Reaction 2 Reaction 3

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4. When 50.0 mL of 1M HCl is mixed with 50.0 mL of 1M NaOH, the temperature of the solution increases from 22.0°C to 26.0°C. Calculate the heat released by this reaction.

• Assume that the densities of the solutions are 1.00 g/mL, and the specific heat of the solutions is the same as the specific heat of pure water.

• NOTE: If you need help, see Page 564 of your text.

5. Create a data table that organizes all if the data given in the previous question.

6. Write a procedure to carry out the experiment described in question 1. Include all steps as a numbered list and underline materials.

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Lab Report Format To complete this lab, you will complete a lab report, using this sheet to guide you. Your final lab report should be typed and submitted in class on the due date. The following sections should be completed, in order, as they appear below. COVER SHEET: A cover sheet with:

• Title of the lab

• Your name

• Your partners’ names

• Due date of the lab report

• Class period

PURPOSE: What are we trying to determine/ do in this experiment? PROCEDURE: A step by step procedure for setting up the experiment and collecting data over the course of the experiment. Directions should be numbered; and read something like a recicpe. Underline any materials you will need once you have written the procedure.

• This should include a general overview on how to use LoggerPro to collect data. DATA: Organize ALL data into a neat data table. This means you will need in depth observations. Things to observe:

• Measurements needed for calculations

• Observations

• Possible sources of error

CONCLUSION: Answer the following questions using complete sentences. You should use at least 5 sentences for each question. For calculations, show all work, including units. This is worth the most points; therefore you should put A LOT of effort into this part.

1. Using your data, calculate the heat (enthalpy) of neutralization. 2. Write a balanced chemical equation for the reaction in this experiment (including heat,

placed on the correct side of the arrow as endo or exo). 3. Explain possible sources of heat loss (error) and how these affect your calculated heat of

neutralization. 4. How would the temperature change and the calculated heat of neutralization vary if the

volumes remained the same but the concentrations of the acid and the base were doubled? Explain.

5. How would the temperature change and the calculated heat of neutralization vary if the concentrations remained the same but the volume of the acid and base was cut in half? Explain.

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Grading Rubric Cover Page

• Title of the lab

• Your name

• Your partners’ names

• Due date of the lab report

• Class period

/2

Purpose

• Clear statement about what we set out to do with this lab

/3

Procedure

• Step by step, repeatable, clear

• Materials are underlined in procedure

• Complete, no steps skipped or assumed

/10

Data

• Table is neat, organized, readable, complete

• Reflects student understanding of lab concepts and practices

• Quality of observations

/10

Conclusion

• Question 1: 5 points





/25

TOTAL:

/50

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CW 12: Bond Enthalpies

The bond enthalpy is the energy required to break a chemical bond, given in units of kJ/mol. The table below contains some common bond enthalpies.

Single Bonds (kJ/mol) C–H 413 N–H 391 O–H 463 F–F 155 C–C 348 N–N 163 O–O 146 C–N 293 N–O 201 O–F 190 Cl–F 253 C–O 358 N–F 272 O–Cl 203 Cl–Cl 242 C–F 485 N–Cl 200 O–I 234 C–Cl 328 N–Br 243 Br–F 237 C–Br 276 Br–Cl 218 C–I 240 H–H 436 S–H 339 Br–Br 193 C–S 259 H–F 567 S–F 327 H–Cl 431 S–Cl 253 I–Cl 208 Si–H 323 H–Br 366 S–Br 218 I–Br 175 Si–Si 226 H–I 299 S–S 266 I–I 151 Si–C 301 S–N 464 Si–O 368 Multiple Bonds (kJ/mol)

C=C 614 N=N 418 O=O 495 C≡C 839 N≡N 941 C=N 615 N=O 607 S=O 523 C≡N 891 S=S 418 C=O 799 C≡O 1072

To find the ΔH of a reaction by bond enthalpies, you need only to apply the correct sign and add the ΔH of the bonds being broken and the bonds being formed.

• Bond breaking is an endothermic process (+ΔH)

• Bond forming is an exothermic process (-ΔH)

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1. Use bond enthalpies to determine the ΔH for the combustion of propane.

Endothermic Change for Bond Breaking Exothermic Change for Bond Forming

Bond # Bond Enthalpy Product Bond # Bond Enthalpy Product

C-H

-----

C=O -----

C-C

O-H

O=O

TOTAL:

TOTAL:

2. Use the information in the previous problem to complete the energy diagram.

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Use bond enthalpies to determine ΔH for the following reactions. Then draw the energy diagram.

3. Answer: –104 kJ

4. Answer: +20 kJ

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CW 13: Hess’s Law

Sometimes it is difficult to measure the enthalpy change for a reaction. The reaction may be too slow to measure in a reasonable amount of time, or it may be an intermediate step in a series of reactions. Hess’s law of heat summation allows you to determine the heat of reaction indirectly by using the known heats of reaction of two or more thermochemical equations. You can add the heats of several reactions to find the heat of the desired reaction. Consider the conversion of diamond to graphite. This reaction is too slow to measure directly.

C(s, diamond) → C(s, graphite) ΔH = ? (a) The enthalpy change is known for the following reactions:

C(s, diamond) + O2(g) → CO2(g) ΔH = -393.5 kJ (b) C(s, graphite) + O2(g) → CO2(g) ΔH = -395.4 kJ (c)

1. Write reaction (c) in reverse, starting with the products and creating the reactants.

Because you are reserving the direction of the reaction, you must also reverse the sign of the ΔH value. This reverse equation is now equation (d).

ΔH = (d)

2. Write reaction (b) and the reversed reaction (d) in the boxes below. Cancel out items that appear on both sides of the arrow to get the desired reaction from above. Calculate the ΔH by adding up the ΔH values for reaction (b) and reaction (d).

(b)

ΔH =

(d)

ΔH =

(a)

ΔH =

Normal algebraic relationships may be applied to chemical equations. For example, 1 mole of A left of the arrow cancels 1 mole of A right of the arrow, leaving behind 2 moles of A.

3A + B → C + D C + D → 1A + E

2A + B → E You may multiply a reaction by any whole positive number, so long as you multiply the ΔH by the same whole number.

A + B → C ΔH = 10 kJ 2A + 2B → 2C ΔH = 20 kJ

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3. Find ΔH for the reaction 2 Al(s) + Fe2O3(s) → 2 Fe(s) + Al2O3(s) from the following data:

2 Al(s) + 3

2O2(g) → Al2O3(s) ΔH = –1676.0 kJ

2 Fe(s) + 3

2O2(g) → Fe2O3(s) ΔH = –822.1 kJ

Answer: –853.9 kJ

4. Calculate ΔH for the reaction S(s) + O2(g) → SO2(g) from the following data: 2 SO2(g) + O2(g) → 2 SO3(g) ΔH = –196 kJ 2 S(s) + 3 O2(g) → 2 SO3(g) ΔH = –790 kJ

Answer: –297 kJ

5. Calculate ΔH for the reaction 2 F2(g) + 2 H2O(l) → 4 HF(g) + O2(g) from the following data:

H2(g) + F2(g) → 2 HF(g) ΔH = –537 kJ 2 H2(g) + O2(g) → 2 H2O(l) ΔH = –572 kJ

Answer: –502 kJ

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CW 14: Rate of Reaction

Collision Theory According to collision theory, atoms, ions, and molecules can react to form products when they collide if the particles have enough kinetic energy and collide with the correct orientation. If the colliding particles do not meet these conditions, they will simply bounce apart, unchanged.

1. Consider the pictures below.

A.

B.

a. Which picture shows a successful collision? Justify your answer.

b. Compare the intermediate step for both reactions. This is called the activated complex. Which one more closely resembles the products of this reaction?

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Activation Energy and the Activated Complex At warmer temperatures, particles have greater average kinetic energy. If their kinetic energy is greater than the activation energy of the reaction, their collisions will result in the formation of products. When particles collide with enough energy and in the right orientation, they form an activated complex, which only lasts for about 1x10-13 seconds. This brief existence ends with either the reformation of reactants or with the formation of products.

2. Consider the graphs below, which show the energy changes for two reactions.

a. Is energy absorbed or released as a reaction progresses from the reactants to the

activated complex? Explain.

b. Which reaction is endothermic, and which is exothermic? Label each image.

c. Why might a reaction that releases energy (exothermic) absorb some energy before the reaction will begin?

d. Once an activated complex is formed, will it always proceed to form products? Explain.

e. How can activation energy be considered a “barrier” to a reaction?

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Rate of Reaction In chemistry, the rate of a chemical reaction is expressed as the change in the amount of reactant or product per unit time.

3. Complete the diagram. 4. If each box represents the same

time interval, is the reaction rate constant throughout the reaction? How can you tell?

Temperature Usually, raising the temperature speeds up a reaction.

• At higher temperatures, particles move faster.

• The frequency of collisions increases along with the percentage of particles that have enough kinetic energy to slip over the activation-energy barrier.

5. Compare the motion of particles (collisions) in two samples, one at room temperature,

and one at high temperature. When charcoal burns, the carbon in the charcoal reacts with oxygen molecules in the air according to the following reaction:

C(s) + O2(g) → CO2(g) + 393.5 kJ

6. Why does this reaction not occur at room temperature, but will occur if a starter flame is used? What is the relationship between the starter flame and activation energy? Explain in terms of collisions and temperature.

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Concentration Cramming more particles into a fixed volume increases the frequency of collisions, leading to a higher reaction rate.

7. Watch the video at: http://www.youtube.com/watch?v=kw-Lt9-WmTg

8. Compare the rate of reaction when 7.47 g of KI are used and when 14.94 g of KI are used. Which solution had a higher concentration of KI?

When something burns, it reacts with oxygen in a combustion reaction. The picture below shows a weakly burning ember in air. The ember is then placed into a vial containing pure oxygen, where it bursts into flames.

9. Explain these observations in terms of collisions.

10. The atmosphere is about 20% oxygen. Why might it be a problem if it was 90% oxygen?

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Surface Area 11. Which has a greater surface area, one large chunk or many small pieces?

12. Complete the following by finding the total surface area for each sample.

Length of side = 1 cm

Surface area of cube: 𝑆𝐴𝑐𝑢𝑏𝑒 = 6 × (𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑖𝑑𝑒)2

Number of cubes: 1 Total surface area:

𝑆𝐴𝑡𝑜𝑡𝑎𝑙 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑢𝑏𝑒𝑠 × 𝑆𝐴𝑐𝑢𝑏𝑒

Length of side = 0.50 cm


Number of cubes: 8 Total surface area:

𝑆𝐴𝑡𝑜𝑡𝑎𝑙 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑢𝑏𝑒𝑠 × 𝑆𝐴𝑐𝑢𝑏𝑒

Length of side = 0.25 cm


Number of cubes: 64

Total surface area: 𝑆𝐴𝑡𝑜𝑡𝑎𝑙 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑢𝑏𝑒𝑠 × 𝑆𝐴𝑐𝑢𝑏𝑒

13. The larger the surface area of a reactant, the more places available for collisions to

occur. Which will burn the fastest; a tightly or a loosely balled up piece of steel wool?

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Catalysts Catalysts permit reactions to proceed along a lower energy path by lowering the activation energy barrier of a reaction, which increases their rate. For example, the rate of reaction of hydrogen and oxygen at room temperature is negligible. But with a small amount of platinum catalyst, the reaction is rapid.

𝐻2(𝑔) + 𝑂2(𝑔)𝑃𝑡→ 2𝐻2𝑂(𝑙)

Catalysts are written above the yield arrow, as they are not consumed during the reaction.

14. How does using a catalyst change the amount of energy needed for products to form?

15. Does the catalyst change the amount of energy released in this reaction (ΔH)? Explain.

16. Along which reaction paths are reactants converted more rapidly into products?

Journal Write 7 Create a “rule of thumb” to explain the relationship between collisions and rate of reaction. Based on this rule of thumb, how might increasing the pressure on a reaction between two gasses affect the rate of reaction?

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Energy Transformation Project (Group)

Introduction and Theme of the Project: Energy is a property of objects which can be transferred to other objects or converted

into different forms but never created nor destroyed. Humans have developed various means of using energy to our benefit, such as the batteries in cell phones, solar cells, and geothermal electricity generation. We have even used the nuclear energy stored in atoms to power entire cities. Your goal is to build off of concepts of energy to design, build and refine a device that will convert chemical energy to another form of energy of your choosing. Directions: Initial Group Tasks:

1. Groups will be composed of 3 to 4 members. 2. Determine the source of chemical energy your group wishes to convert. This could be a

chemical reaction or a phase change. You may not use a battery unless you make one. 3. Design a means to convert your chemical energy into a different form. You must include

at least two energy transformations.

4. Submit a proposal to your instructor proving your completion of the above and

requesting permission to build your prototype. Proposal Due Date: ______________________ (see front of packet) Follow-Up Group Tasks:

5. Receive feedback on your proposal from your instructor. 6. Build a working prototype of your energy converting device. Depending on your choice

of chemical reaction, you may be required to do much of your work at school during NEST or after school.

7. Test your device to insure it works and fix any problems you discover. 8. Create a video showing your device in action. 9. Present your video to your class using the rubric on the next page.

Presentation Date: ______________________ (see front of packet).

Chemical Energy

Different form of energy

Different form of energy

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Energy Transformation Project Rubric: CATEGORY 10 8 6 4 2 0

PROPOSAL

Diagram Diagram is neat with clear labeling for all components. All required materials are listed.

Diagram is neat with clear labeling for most components. All required materials are listed

Diagram provides clear labeling for most components. Most materials are listed.

Diagram is inadequately labeled. Some materials are listed.

Diagram is inadequately labeled. Materials are not listed.

No effort

PRESENTATION

Modification/Refinement of device

Clear evidence of refinements, resulting in a very well-functioning device. Minimal energy loss.

Some evidence of refinements, resulting in a functioning device. Some energy loss.

Little evidence of refinements, but still resulting in a functioning device. Much energy is lost.

Device was refined, but still does not function. Much energy is lost.

Device does not function as intended but was built.

No effort

Video and Explanation

Video clearly shows the energy conversion and is very well explained.

Video clearly shows the energy conversion and is very somewhat well explained.

Video shows the energy conversion and is somewhat well explained.

Video shows the energy conversion and is poorly explained.

Video does not show the energy conversion and is poorly explained

No effort

Scientific Knowledge/ Content

Explanations by all group members indicate a clear and accurate understanding of scientific principles underlying the construction and modifications.

Explanations by all group members indicate a relatively accurate understanding of scientific principles underlying the construction and modifications.

Explanations by most group members indicate relatively accurate understanding of scientific principles underlying the construction and modifications.

Explanations by several members of the group do not illustrate much understanding of scientific principles underlying the construction and modifications.

Explanations by all members of the group do not illustrate understanding of scientific principles underlying the construction and modifications.

No effort

Presentation Quality and Preparedness

Student is completely prepared and has obviously rehearsed. Presentation is expertly edited for content, grammar, and format.

Student seems pretty prepared but might have needed a couple more rehearsals. Presentation is edited for content, grammar, and format.

The student is somewhat prepared, but it is clear that rehearsal was lacking. Presentation is edited for content, grammar, and format, but many show some errors.

Student does not seem at all prepared to present. Presentation is edited for content, grammar, and format, but many show many errors.

Student is not prepared to present. Presentation seems sloppy or “thrown together.”

No effort

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Reference Materials

Periodic Table

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Polyatomic Ions Ion Name Ion Name

H3O+ hydronium CrO42– chromate

Hg22+ dimercury(I) Cr2O7

2– dichromate

NH4+ ammonium MnO4

– permanganate

C2H3O2–

CH3COO– acetate

NO2– nitrite

NO3– nitrate

C2O42– oxalate O2

2– peroxide CO3

2– carbonate OH– hydroxide

HCO3– hydrogen (bi)carbonate CN– cyanide

PO43– Phosphate SCN– thiocyanate

ClO– hypochlorite SO32– sulfite

ClO2– chlorite SO4

2– sulfate ClO3

– chlorate HSO4– hydrogen sulfate

ClO4– perchlorate S2O3

2– thiosulfate

Specific Heats Substance J/(g∙°C) cal/(g∙°C)

Water (liquid) 4.18 1.00

Water (gas) 1.9 0.45 Water (solid) 2.1 0.50

Ethanol 2.4 0.58 Chloroform 0.96 0.23

Aluminum 0.90 0.21

Iron 0.46 0.11 Silver 0.24 0.057

Mercury 0.14 0.033

Heats of Physical Change Substance ∆Hfus (kJ/mol) ∆Hvap (kJ/mol)

Ammonia (NH3) 5.66 23.3

Ethanol (C2H6O) 4.93 38.6 Hydrogen (H2) 0.12 0.90

Methanol (CH4O) 3.22 35.2 Oxygen (O2) 0.44 6.82

Water (H2O) 6.01 40.7

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Average Bond Enthalpies Single Bonds (kJ/mol) C–H 413 N–H 391 O–H 463 F–F 155 C–C 348 N–N 163 O–O 146 C–N 293 N–O 201 O–F 190 Cl–F 253 C–O 358 N–F 272 O–Cl 203 Cl–Cl 242 C–F 485 N–Cl 200 O–I 234 C–Cl 328 N–Br 243 Br–F 237 C–Br 276 Br–Cl 218 C–I 240 H–H 436 S–H 339 Br–Br 193 C–S 259 H–F 567 S–F 327 H–Cl 431 S–Cl 253 I–Cl 208 Si–H 323 H–Br 366 S–Br 218 I–Br 175 Si–Si 226 H–I 299 S–S 266 I–I 151 Si–C 301 S–N 464 Si–O 368 Multiple Bonds (kJ/mol)

C=C 614 N=N 418 O=O 495 C≡C 839 N≡N 941 C=N 615 N=O 607 S=O 523 C≡N 891 S=S 418 C=O 799 C≡O 1072

1 48 class: unit 4: it’s getting hot in here · 04.02.2020 · 7. use a utility clamp to obtain...

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