1. Aim: How to measure the amount of heat released during a phase change
Do Now:
Is ice melting an exothermic or endothermic process? Explain.

2. Heat of Solidification
The amount of heat needed to change a liquid to a solid at constant temperature
Hsolidification= - Hfusion
q=mHsol
The heat of solidification for water is -334 joules per gram

3. Heat of Condensation
The amount of heat needed to convert a gas to a liquid at constant temperature.
Hcondensation = -Hvaporization
q=mHcon
The heat of condensation for water is joules per gram

4. Practice What is the heat of solidification for 3.4 g of water?
2. How much energy is released to the environment by 50.0 grams of condensing water vapor?
3. Is freezing endothermic or exothermic? Explain.

5. Temperature (oC) H2O Gas Gas - Liquid Liquid Liquid - Solid Solid 130
100
Gas - Liquid 3
Temperature (oC) H2O
Liquid 4 5
Liquid - Solid
Solid
-40
Heat Released

6. Cooling Curve The cooling curve is the reverse of the heating curve.
The temperature of the gas is lowering; kinetic energy is decreasing.
When gas changes to liquid (condensation), the temperature stays the same. There is a change in potential energy; potential energy is decreasing.
3. The temperature of the liquid is lowering; kinetic energy is decreasing.

7. Cooling Curve
4. When liquid changes to solid (solidification), the temperature remains the same. There is a change in potential energy; potential energy is decreasing. 5. The temperature of the solid is lowering; kinetic energy decreases.

8. Stearic Acid is a waxy solid at room temperature. It comes from animal
and vegetable fats and oils. It is used as an ingredient in soap, candles,
and cosmetics.
A sample of stearic acid was placed in a heat resistant test tube and
heated to 95 Celsius, which point the stearic acid was completely
liquified. The test tube was placed in a beaker of ice water, and the
temperature monitored until it reached 40 Celsius

9. Answer the following:
1. What is the freezing temperature of stearic acid? What is its melting
temperature?
2. Between which two points is stearic acid freezing?
***3. Compare the melting temperature of stearic acid to the melting temperature of water. Which substance has stronger intermolecular forces? How do you know?