Warm Up1) Draw the heating curve we got

during the lab. Label the parts of the curve to show where phase energy is increasing and where thermal energy is increasing. 2. You have a tea kettle of water boiling on a stove. If you turn up the burner would the temperature of the water change? Explain your answer.

Essential QuestionsEQ: How do we determine the amount of energy that enters or leaves a system?HOT Q1: Why does a seat belt get more hot than a water bottle?HOT Q2: What does the law of conservation of energy state? HOT Q3: What are the 3 eqns we use to find the amount of energy absorbed or released?

Agenda• Warm Up• Agenda• Breaking down yesterday’s lab• Demo: Heat Capacity• Exit Ticket

Label the parts of the curve to show where phase energy is increasing and where

thermal energy is increasing.

Why does this make sense?

• HEAT is constant but the temperature changes at a weird rate.

• WHY? Because of the difference between thermal energy and phase energy.– Thermal energy changes temperature– Phase energy breaks down phases

Practice

11. When a sample of liquid is warmed, its thermal energy

a. increasesb. decreasesc. remains the samed. varies depending on the pressure

12. While a sample of liquid is boiling, its thermal energy

a. increases.b. remains the same.c. decreases.d. is transferred into interaction energy.

•

13. During region C the thermal energy is .

A.IncreasingB.DecreasingC.The sameD.Zero

• 14. During region B the thermal energy is

A.IncreasingB.DecreasingC.The sameD.Zero

15. During region A the phase energy is .

A.IncreasingB.DecreasingC.The sameD.Zero

16. During region C of the graph above the energy being absorbed is

a. increasing the speed of the water moleculesb. increasing the distance between the water molecules and

reducing their phase energy.c. increasing the distance between the water molecules and

increasing their phase energy.d. decreasing the speed of the water molecules

What do we think a cooling curve looks like?

Demo: Dollar Dollar Bills

• Background Info: – Law of Conservation of Energy: Energy is neither

created nor destroyed, it is only transferred.

• Eye Level:

• Particle Level:

Demo: Dollar Dollar Bills

Consensus:Heat capacity (also called “specific heat”) = amount of energy required to raise the temperature of one gram of that substance by one degree Celsius

• We measure energy in joules (J)

Notes

Demo:

• It’s a hot summer day. You get into your car. The seatbelt is BURNING hot (ouch!)

However, a bottle of water you left in the back seat is only slightly warm.

WHY????!

Heat Capacities of Common Substances

Substance Heat capacity (J/g C)Water (l) liquid 4.18Water (s) solid 2.1Alcohol 2.44Aluminum 0.897Gold 0.129

• It takes 4.18 joules to raise the temperature of 1 g of liquid water by 1 C.

• We can write this value as:

Suppose that we have a larger sample of liquid water. How much energy would it take to raise the temperature of 5 g of water by one degree Celsius?

How much energy would it take to raise the temperature of 5 g of water by 2 degrees Celsius?

Cg

J

1̊1

18.4

Listen.

You just derived this equation:

q = quantity of energy transferred (in J)m = mass (in g)C = heat capacity (J/g ⁰C)∆T = change in temperature (in⁰ C)

∆T = Tfinal - Tinitial

TmCq p

Write!

How much energy does it take to raise the temperature of 5 g of water by 2 degrees celsius?

How could we graph this on a heating/cooling curve?

Heat EquationsEnergy Constants (H2O)• Heat of fusion, Hf= 334 J/g

(amount of energy required to melt or freeze 1 g of H2O)

• Heat of vaporization, Hv = 2260 J/g(amount of energy required to evaporate or condense 1 g of H2O)

• Heat capacity (C) of solid H2O = 2.1 J/g˚C

• Heat capacity (C) of liquid H2O = 4.18 J/g˚C

TmCq p

fmHq

vmHq

Notes

Which Heat Equation?What is

happening to the substance?

Use This Equation

Freezes or melts

Evaporates or condenses

Temperature changes

fmHq

vmHq

TmCq p

Notes

Wait! Which equation do I use??!!

1. A cup of hot chocolate (270 g) cools from 60˚C down to comfortable room temperature 20.˚C. How much energy does it release to the surroundings?

First, before you do any math, you need to determine what changes are taking place.

Steps

1. What changes are taking place? (Is temperature changing? Is phase

changing?)2. Which heat equation? 3. Identify variables.4. Plug in and solve.

2. A 110g cup of water spills on your kitchen floor. If all of the water is evaporates, how much energy did the water absorb from the surroundings?

1. What changes are taking place? 2. Which heat equation?

Partner PracticeYou accidentally left your flavor-ice popsicle, with a mass of 43g at 0˚C,on a park bench during the summer. By the time you got back from the basketball court it is totally melted. How much energy must be absorbed by the ice in order for it to melt all the way? (assume no temperature change)

1. What changes are taking place? 2. Which heat equation?

Partner Practice

A cup of water, 270 g, at 100C evaporates when left outside on a summer day. How much energy did the cup of water absorb? (assume no temperature change)1. What changes are taking place?

2. Which heat equation?

Partner Practice

• Add one more problem.

Exit Ticket

• There is a 150 g puddle of water at 0C outside. It freezes overnight. How much energy was required to freeze the water?

• A 320 g cup of iced tea warms on a summer day from 10 degrees Celsius to 40 degrees Celsius. How much energy was required?

HW: WKSHT #2

Exit Ticket1. Identify region IV of the heating curve on the

board.A. SolidB. Solid-LiquidC. LiquidD. Liquid-Gas

HW: WKSHT #2