1

Unit 10: Gas Laws Name:

Class Period: Test Date: February 27th

Monday Tuesday Wednesday Thursday Friday

February 9 Computer Lab Stoichiometry Review

10 Stoichiometry Test Review HW: Study for Test Tomorrow!

11 Stoichiometry Test

12 Pressure & Kinetic Theory of Gases HW: p.4 Bring an empty soda can to class tomorrow

13 Combined Gas Law Soda can activity HW: p.8 Study for Cumulative Retest

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Holiday!!

17 Cumulative Re-Test

18 Chem Think Gas Laws Tutorial- Computer Lab- Massie B-112 Boyle’s, Charles’, and Avogadro’s Law- HW: pp.13 – 14 Burrough, Maldonado, Smith, Oetgens, Thompson

19 Boyle’s, Charles’, and Avogadro’s Law- Massie today HW: pp.13 – 14 Chem Think Gas Laws Tutorial- Computer Lab- Burrough B-112 Maldonado B-122 Smith- B-112 Oetgens B-118 Thompson B-120

20 Gas Laws Lab/Activity Begin working on Study Guide- pgs. 23-27 Study for Quiz on Monday

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Quiz Dalton’s Law of Partial Pressures HW: Pg. 16 Study Guide- pgs. 23-27

24 Ideal Gas Law HW: p.19 Study Guide- pgs. 23-27

25 Stoichiometry with Gas Laws HW: p.22 and study guide (pp.23-27)

26 Review for Test Study Guide Due TODAY!!

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Gas Laws Test

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Pressure

1. What is the definition of pressure?

2. What causes pressure?

3. Which shoes create the most pressure? How does changing the area of contact affect the amount of pressure

exerted by an object?

4. What are the units used to measure pressure?

5. How do I convert between units of pressure?

atm = mmHg = kPa = psi

6. How many kilopascals are equivalent to 880 mmHg?

7. Calculate the number of pounds per square inch (psi) that are in 2.60atm.

Temperature – ALWAYS use absolute temperature (Kelvin) when working with gases.

Conversion:

K = °C + 273

Practice problems:

32°C = __________ K How much is 75°C in Kelvin?

3

The Behavior of Gases and the Kinetic Theory

Kinetic refers to __________________.

The energy an object has, because of its motion, is called __________________________

The Kinetic theory states that “the tiny particles in all forms of matter are in

______________________________.”

Watch the video segment (Kinetic Molecular Theory in the video Standard Deviants School Chemistry:

Molecular Geometry) on Discovery Education and fill in the missing information

http://app.discoveryeducation.com/search?Ntt=standard+deviants+gas

Basic assumptions of the kinetic theory as it applies to gases are:

1. A gas is composed of particles, usually molecules or atoms that are _______ ___________ from one

another in comparison with their own dimensions. Particles are relatively far apart from one another and

between them is ______________ ______________.

2. Gas molecules are in ________________ ______________ ______________. They travel in straight

paths (unless they collide with a wall of a container) and move independently of each other.

3. The molecules exert no force on each other or on the container until they _____________ with each

other or with the walls of the container.

4. The average kinetic energy of the molecules of a gas is proportional to the _______________________.

5. Every time a molecule collides with the wall, it exerts a __________________

on it which we call _____________________.

Applying this knowledge we know…

Gases fill their containers regardless of the ______________ and

_______________________ of the containers.

Because there is so much space between particles, gases are

______________________________________. Because gases are

_______________________, they are used in automobile _______________ and

other safety devices designed to ______________ the _____________ of an

impact.

All _______________ are perfectly ___________. This means that during

collisions kinetic energy is transferred without loss from one particle to another, and

total kinetic energy remains _________________.

4

The average speed of oxygen molecules in air at 20oC is 1700 km/h. At these high speeds, the odor

molecules from a hot pizza in Washington, D.C., should reach Mexico City in about 106 minutes. Why

doesn’t this actually happen? __________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

Questions:

A. What happens when a closed container is inflated?

B. A gas inside a bicycle tire exerts a pressure of 35 pounds per square inch (psi). How much air must be

pumped into the tire to produce a pressure of 70 psi?

** The relationship between amount of gas and pressure is proportional, assuming the volume & temperature

stay the same.

C. What happens to pressure when a closed container is deflated?

(Note: Gas particles move from region of higher pressure to lower pressure until equilibrium is reached.)

HOMEWORK Day 1 - Practice Problems on Pressure & Temperature Conversions Show all work! Record your answer with the correct number of significant figures and units!

1. Calculate the pressure of 1.3atm in mmHg.

2. Convert 56kPa to psi.

3. How many atmospheres are equivalent to 230kPa?

4. What is 560K on the Celsius scale?

5. Water boils at 100oC. What is the boiling point of water in Kelvin?

5

COMBINED GAS LAW

The Combined Gas Law helps us explain what happens to gases as the pressure, temperature, and volume changes in

respect to moles of a substance.

Letter or

Number Variable Name Unit Conversions

P

V

6

n*

T

1

2

*NOTE: If “n” is not given in a problem, assume it to be 1 mole.

Temperature must be in .

Remember: STP = ____ atm and ________ K or ____°C

Guided Practice:

1. A hot air balloon has a volume of 7500L at 270K and a pressure of 1.2 atm. What will be the volume of the

balloon if the pressure changed to 0.90atm and the temperature decreases to 230K?

Givens and Unknowns:

P1 =

V1 =

n1 =

T1 =

P2 =

V2 = unknown

n2 =

T2 =

Equation:

Substitute & Solve:

7

2. The volume of a gas at STP is 22.4L. At 12oC, the volume of the balloon changes to 55.0L. What is the new

pressure?

Givens and Unknowns:

P1 =

V1 =

n1 =

T1 =

P2 =

V2 =

n2 =

T2 =

Equation:

Substitute & Solve:

=

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Homework - Combined Gas Law Practice

1. A 5.00 L air sample at 170 K has a pressure of 107 kPa. What is the new pressure if the temperature is

raised to 548 K and the volume expands to 7.00L?

2. A gas at 880mmHg and 298K occupies a container with an initial volume of 1.00 L. The pressure increases to

1980mmHg as the temperature rises to 398K. What will be the new volume?

3. The volume in a gas filled balloon is 30.0 L at 40°C and 3.6 atm of pressure. What volume will the balloon

occupy at STP?

4. A container has an initial volume of 4.5 L, a pressure of 450 kPa and is at a temperature of 15 oC. If the

container is expanded to 6.5 L while the pressure is decreased to 125 kPa, find the resulting temperature.

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Soda Can Activity

OBJECTIVES

Students will demonstrate the effects of air pressure.

Students will demonstrate that as a gas is heated it expands and as it cools it will contract.

MATERIALS

an empty aluminum soft-drink can

a 1000 mL beaker

a pair of beaker tongs

hot plate

PROCEDURE

1. Fill the large beaker with ice cold water.

2. Put 15 – 20 milliliters of water into the empty soft-drink can.

3. Heat the can on the hot plate at the highest setting. When the water boils, a cloud of condensed vapor will

escape from the opening in the can. Allow the water to boil for about two minutes. Do not let all of the

water evaporate.

4. Using the beaker tongs, grasp the can and quickly invert it and dip it into the water in the pan. Be careful

of the hot water!

5. Record your observation.

6. Clean up your lab station.

OBSERVATION

CONCLUSION

Explain why the can was crushed (discuss the relationships between pressure, volume, and temperature). Why did

you have to heat the can up in order for the can to be crushed?

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Boyle’s Law and Charles’ Law

The Effect of Changing Size of Container – Boyle’s Law WHAT IF…temperature and moles do not change and we just look at the relationship between pressure and

volume. Our equation would look like this:

P1V1 = P2V2 Boyle’s Law

Boyle’s Law states that at a constant temperature, the volume of a gas is inversely proportional to the pressure

exerted by that gas.

Examples:

a. If a gas is compressed from 2L to 1L, the pressure will

_____________ by a factor of 2.

b. If a gas is expanded from 1L to 3L, the pressures will

_______________ by a factor of 3.

c. Gases cool when they expand and heat when they compress.

Why?

Thus, if you forget to wear your suit in space, you

will_________________!!!

Example Problems

1. The pressure of a 3.5L balloon was determined to be 1.5atm. Assuming that the temperature remained

constant, what would be the volume of the balloon if the pressure was decreased to 0.45atm?

2. At 45oC, a certain container of gas has the volume of 580mL and a pressure of 980mmHg. What would be

the new volume of the gas at 250 mmHg and 45oC?

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The Effect of Temperature changes on Volume – Charles’s Law

As the gas inside a balloon _________________, the average KE of

molecules __________.

With fewer and less collisions, the gas molecules move ________

together and occupy a _________ volume than they previously did.

The ___________________, assuming no change in the amount of

gas and pressure.

Charles’ Law

Charles law states: At a constant pressure, the ________________ of a gas is directly _________________

to the __________________ in Kelvin.

GUIDED PRACTICE: Temperature must be in . 1. The temperature of a 0.65L sample of carbon dioxide gas is 580K. If the pressure remains constant, what

is the new volume of the gas if the temperature increases to 1300K?

2. A balloon has a volume of 5.6L at a temperature of 98oC. If the volume of balloon increases to 9.5L, what

will be the temperature of the gas in Celsius? Assume that the pressure remains constant.

2

2

1

1

T

V

T

V

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Avogadro’s Law

Avogadro's Law (Avogadro's theory; Avogadro's hypothesis) is a principle stated in 1811

by the Italian chemist Amedeo Avogadro (1776-1856) that "equal volumes of gases at

the same temperature and pressure contain the same number of molecules regardless

of their chemical nature and physical properties". This number (Avogadro's number) is

6.02 X 1023. It is the number of molecules of any gas present in a volume of 22.4 L and is

the same for the lightest gas (hydrogen) as for a heavy gas such as carbon dioxide or bromine.

Or to put it another way, "the principle that equal volumes of all gases at the same temperature and

pressure contain the same number of molecules.

Thus, the molar volume of all ideal gases, at 0° C and a pressure of 1 atm., is 22.4 liters"

V1 = V2 V = the volume of the gas

n1 n2 n = the amount of substance, in moles, of the gas

Example #1: 5.00 L of a gas is known to contain 0.965 mol. If the amount of gas is increased to 1.80 mol, what

new volume will result (at an unchanged temperature and pressure)?

Example #2: A cylinder with a movable piston contains .005 mol of helium, He, at room temperature. More

helium was added to the cylinder and the volume was adjusted so that the gas pressure remained the same.

How many moles of helium were added to the cylinder if the volume was changed from 2.00 L to 2.70 L? (The

temperature was held constant.)

Example #3:

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Homework – Boyle’s, Charles’, and Avogadro’s Laws Practice

First, identify which gas law you need to use to solve the problem and then solve for the unknown. Be sure

to show all work. For every problem, report your answer with the correct number of significant figures and

the correct units! Remember, temperature must be in KELVINS!!!

1. Gas law: ___________________________________

A sample of carbon dioxide occupies a volume of 3.5 L at 125 kPa. What pressure would the gas exert if

the volume were decreased to 2.00 L? Assume that the temperature remains constant.

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2. Gas law: ___________________________________

A 6.0 L sample at 25 °C and 2.00 atm of pressure contains 0.5 moles of a gas. If an additional 0.25 moles of

gas at the same pressure and temperature are added, what is the final total volume of the gas?

3. Gas law: ___________________________________

When 250 mL of O2 is heated, there is now 310 mL O2 at 273K. What is the original temperature in oC?

4. Gas law: ___________________________________

Your Valentine’s Day balloon has a maximum volume of 5.5 L. Your balloon originally has a volume of 5.2 L at

288K. When you walk into your Chemistry classroom, you realize that they have finally fixed the heat. The

temperature in there is now 320K. Should you worry that your balloon will pop?__________ Support your

answer with calculations!

5. Gas law: ___________________________________

The pressure on anesthetic gas changes from 15.0 atm to 6.0 atm. If the original volume was 12.0 L, what

will be the new volume of the anesthetic gas after the pressure has been decreased?

6. Gas law: ___________________________________

You have 2.00 L of dry H2 at STP. How many moles is this?

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Dalton’s Gas Law of Partial Pressures

Partial pressure of a gas in a mixture of gases is the pressure which that gas would exert if it were the

only gas present in the container.

Dalton's Law of Partial Pressures states that the total pressure in a gas mixture is the sum of the partial

pressures of each individual gas.

Ptotal = Pgas a + Pgas b + Pgas c + etc

Dalton's Law of Partial Pressures assumes each gas in the mixture is behaving like an ideal gas.

Ptotal = Pgas a + Pgas b

=

+

Example Problems

1. Air contains oxygen, nitrogen, carbon dioxide, and trace amounts of other gases. What is the partial

pressure of oxygen (Poxygen) at 101.3kPa if the partial pressures of nitrogen, carbon dioxide, and other gases

are 79.10kPa, 0.040kPa, and 0.94kPa, respectively.

2. A mixture of gases contains oxygen, nitrogen, and helium. The partial pressure of oxygen is 2.1atm. The

partial pressure of nitrogen in 0.21atm, and the partial pressure of helium is 7.80atm. Determine the total

pressure of this mixture.

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Homework for Dalton’s Gas Law of Partial Pressures

For each problem, calculate the pressure using correct units. Box final answer. SHOW ALL WORK!!

1. Oxygen gas from the decomposition of potassium chlorate, KClO3, was collected by water displacement.

2 KClO3 2 KCl + 3 O2

What is the partial pressure of oxygen collected if the barometric pressure (total) was 731.0 torr and the

vapor pressure of water at 20.0C was 17.5 torr?

P1 =

Ptotal =

P2 =

2. A sample of nitrogen gas was collected over water at a temperature of 23.0C. What is the partial

pressure of nitrogen if the atmospheric pressure (total) was 785 mmHg and the vapor pressure of water

was 21.1 mmHg?

P1 = Ptotal =

P2 =

3. At high altitudes, pilots have to supplement their supply of oxygen. In this mixture, there are oxygen and

nitrogen gases. If nitrogen’s partial pressure is 250mmHg, calculate the partial pressure of oxygen if the

total pressure is 710mmHg.

4. Saturn’s atmosphere is composed of hydrogen and helium. If the partial pressures of the gases are

25.0atm and 1.2atm, respectively, what is the total pressure?

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Ideal Gas Law

An ideal gas is one that follows the gas laws at ____________________________.

Such a gas would have to conform precisely to the assumptions of _______________ ________________.

As you probably suspect, there is ______________ for which this is true. An ideal gas

__________________ exist. Nevertheless, at many conditions of temperature and pressure,

___________________ behave very much like an ideal gas.

An important behavior of real gases that differs from that of a hypothetical ideal gas is that real gases can be

__________________ and sometimes _______________ by cooling and by applying pressure. Ideal gasses

cannot be. For example, when water vapor is cooled below 100oC at standard atmospheric pressure, it

condenses to a liquid. The behavior of other real gases is similar, although lower temperature and greater

pressures may be required.

****Gases behave ideally at __________________________________________________.

If we look at one side of the Combined Gas Law:

P V

n T

and solve it for one mole at STP, you would get a “constant” (symbolized as R).

(101.3 kPa)(22.4 L) = 8.31 (L . kPa)/(K . mol)

(1 mole)(273 K)

We call this the ideal gas constant (R):

If pressure is measured in: The ideal gas constant (R) is:

kPa 8.31 (L . kPa)/(K . mol)

atm 0.0821 (L . atm)/(K . mol)

mmHg 62.4 (L . mmHg)/(K . mol)

torr 62.4 (L . torr)/(K . mol)

SO…

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GUIDED PRACTICE:

1. Calculate the number of moles of oxygen in a 12.5 L tank containing 250 atm, measured at 22oC.

Givens and Unknowns:

P =

V =

n =

R =

T =

Equation:

PV = nRT

Substitute & Solve:

2. If 4.5 g methane gas (CH4) is introduced into an evacuated 2.00 L container at 35oC, what is the pressure

in the container, in atm?

Givens and Unknowns:

P =

V =

n =

R =

T =

Equation:

PV = nRT

Substitute & Solve:

3. A balloon is filled with 0.34 moles of pure nitrogen. If the balloon is at 37 oC and is under pressure of 100

kPa, calculate the volume of the balloon.

Givens and Unknowns:

P =

V =

n =

R =

T =

Equation:

PV = nRT

Substitute & Solve:

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Homework for Ideal Gas Law

1. 16 L of carbon dioxide is at a temperature of 45º C and a pressure of 85 kPa. Calculate the number of moles of

gas present.

2. The pressure inside a balloon filled with 168 g of nitrogen (N2) is 95 kPa with a temperature of 15º C. Calculate

the volume of the balloon.

3. 76 L of compressed oxygen is at a temperature of 330 K. If there are 7.3 mols of oxygen in the container,

calculate the pressure (in atm) inside the container.

4. What mass of carbon dioxide will occupy 5.5 L at 5.0C and 0.74 atm?

5. If a cave has a volume of 5.4 x 106 L of air at a pressure of 140 kPa and it is determined that there are

3.0 x 105 mols of CO2 present, calculate the temperature inside the cave.

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Ideal Gas Law and Stoichiometry of Gases

Ideal Gas Law and Stoichiometric Problems

In industry and in the laboratory, many important chemical reactions involve gases. A common laboratory

experiment that produces small amounts of hydrogen gas involves the reaction of an active metal with a strong

acid. This reaction can be represented by the general equation:

M (s) + HA (aq) MA (aq) + H2 (g)

where "M" represents the metal, "HA" the acid, and "MA" the salt formed between the metal and the anion of the

acid.

It is important to be able to perform stoichiometric calculations for gas reactions. Stoichiometric calculations

involving gases are identical to those involving solids and liquids with one important exception. For chemical

reactions involving only solids and/or liquids, the amounts of reactants and products are usually expressed in grams;

however, for chemical reactions involving gases, the amounts of gaseous reactants are usually expressed in liters.

To perform a stoichiometric calculation, the number of liters of a gas reactant must first be converted to moles

using the ideal gas law. For stoichiometric calculations in which the number of moles of gas products has been

calculated, the volume can be calculated using the ideal gas law.

Example 1: 3.00 liters of nitrogen (N2) gas is reacted with excess hydrogen (H2) gas to form ammonia (NH3) gas

at 304K and a pressure of 1.02 atm. How many liters of ammonia gas are formed?

Step 1: Write the balanced chemical reaction.

N2 (g) + H2 (g) NH3 (g)

Step 2: Convert liters of N2 to moles of N2.

NOTE: Since the gas is not at STP, you must convert using the Ideal Gas Law before you can do Stoichiometry!!!

PV = nRT:

Step 3: Convert moles of N2 to moles of NH3 using the mole ratio of the balanced chemical equation.

Step 4: Convert moles of NH3 to liters of NH3 using the ideal gas law.

PV = nRT:

mole • K

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Example 2: Calculate the volume of hydrogen gas produced at 0.0°C and 1.00 atm of pressure by reacting 12.0 g of

zinc metal with excess sulfuric acid.

Step 1: Write the balanced chemical reaction.

Step 2: Convert grams of zinc to moles of H2 using the mole ratio from the balanced equation.

Step 3: Convert moles of H2 to liters of H2 using the ideal gas law.

PV = nRT

Class Practice:

3. How many grams of calcium carbonate will be needed to form 4.29 liters of carbon dioxide? The following

reaction takes place at a pressure of 1 atm and a temperature of 298K.

CaCO3(s) CO2(g) + CaO(s)

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Ideal and Stoichiometry Homework: 1. How many liters of water can be made from 55 grams of oxygen gas and an excess of hydrogen at a pressure of

12.4 atm and a temperature of 850 C?

2H2(g) + O2(g) 2H2O(l)

2. If you burned a gallon of gas (C8H18) (approximately 4000 grams), how many liters of carbon dioxide would be

produced at a temperature of 21.0oC and a pressure of 1.00 atm?

2C8H18(l) + 25 O2(g) 16 CO2(g) + H2O(g)

3. Using the same chemical equation as in #2, how many grams of water would be produced if 20.0 liters of oxygen

were burned at a temperature of 263oK and a pressure of 1.3 atm?

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Gas Laws STUDY GUIDE Due: February 26th

Units of Measurement:

For the following questions, use the following answer choices to indicate what each unit of measurement is

used to measure.

A. Pressure B. Volume C. Temperature

______1. K

______2. atm

______3. mL

______4. kPa

______5. L

______6. oC

______7. psi

______8. mmHg

Kinetic Molecular Theory

A crew was given steam cleaning equipment and asked to steam clean a Tank Car. The interior of the tank car was

washed out & cleaned with steam. Then all the outlet valves were shut and the tank car was sealed. All the

workers went home for the evening and when they returned, the picture below shows what they found.

Explain why this happened using the behavior of gases to support your answer.

Pressure

Answer the following questions related to pressure. For any problems, show all work (using dimensional

analysis) and report your answers with the proper number of units and significant figures.

1 atm = 760 mmHg = 101.3 kPa = 14.7 psi

9. In a sample of gas, what causes pressure? Answer in a complete sentence.

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10. How many millimeters of mercury are in 4.5atm?

11. How many kilopascals are in 76.0 psi?

Relationships among P, V, T and the Number of Gas Particles

Answer the following questions in complete sentences.

12. If temperature is held constant, as the volume increases, the pressure for a given sample of gas will

__________________? Justify your answer on a molecular level.

13. How does increasing the number of gas particles affect the pressure of a gas? Justify your answer on a

molecular level.

14. How does the kinetic energy of a gas change as temperature is increased?

How does this affect the pressure?

Gas Laws and Graphing

15. Define Boyle’s, Charles’, and Avogadro’s Laws.

25

Use the following graphs to answer the next 7 problems.

16. Which graph represents Boyle’s Law?

17. Which graph represents Charles’s Law?

18. Which graph has the same shape as Avogadro’s Law? ___________________________

19. In Graph #1, what is the pressure on 20mL of gas?

20. In Graph #2, what is the volume when the temperature reaches 55K?

21. Which graph represents an inverse relationship?

22. Which graph represents a direct relationship?

Sample Problems

Show all work. Be sure to report your answers with the correct numbers of significant figures and the

correct units. Also, write down the gas law used to solve each problem.

23. What is the volume of a sample of gas that contains 1.2mol at 780K and 1.3atm?

Name of Gas Law used here: ______________________________

0

20

40

60

80

100

0 20 40 60 80 100Press

ure(k

Pa)

Volume (mL)

Graph #1 :The Relationship

between Volume and Pressure

of a Gas

0

50

100

0 20 40 60

Volum

e (L)

Temperature (K)

Graph #2: The Relationship

between Volume and

Temperature of a Gas

26

24. A balloon is heated so that it will expand. Initially, the volume is 56mL at 45oC. If the balloon is heated so

that it expands to 130mL, what is the new temperature in the balloon in degrees Celsius?

Name of Gas Law used here: ______________________________

25. What is the new pressure if a 2.0L sample at 120kPa is reduced to 1.2L assuming that the temperature

remains constant?

Name of Gas Law used here: ______________________________

26. Laughing gas is a mixture of dinitrogen monoxide and oxygen. If the total pressure is 1.2atm, what is the

partial pressure of dinitrogen monoxide given that the partial pressure of oxygen is 0.45atm?

Name of Gas Law used here: ______________________________

27. The Kelvin temperature of a gas was originally doubled. If the initial pressure is 740mmHg, what would be

the new pressure after the temperature was increased?

Name of Gas Law used here: ______________________________

27

28. A 3.45L sample of nitrogen gas is originally at STP. If the temperature is increased to 50oC and the

pressure is raised to 2.3atm, what is the new volume?

Name of Gas Law used here: ______________________________

29. What is the mass of carbon monoxide gas if 0.304L is kept at 0.45atm and 440K?

Name of Gas Law used here: ______________________________

30. A cylinder with a movable piston contains 0.500 moles of helium at room temperature. More helium was

added to the cylinder and the volume was adjusted so that the gas pressure remained the same. How many

moles of helium were added to the cylinder if the volume was changed from 2.00 L to 2.70 L?

Name of Gas Law used here: _____________________________

31. How many grams of AlCl3 must decompose in order to produce 3.10 liters of Cl2 at 50.0C and

98.4 kPa? 2AlCl3 2Al + 3Cl2