1. Aim: How to measure energy absorbed during a phase change??
DO NOW:
1. A g piece of iron absorbs joules of heat energy, and its
temperature changes from 25°C to 175°C. Calculate the specific heat capacity
of iron.
2. How many joules of heat are needed to raise the temperature of 10.0 g of
aluminum from 22°C to 55°C, if the specific heat of aluminum is 0.90 J/g°C?
3. To what temperature will a 50.0 g piece of glass raise if it absorbs 5275
joules of heat and its specific heat capacity is 0.50 J/g°C? The initial
temperature of the glass is 20.0°C.
HW: Worksheet

2. Do-now Solutions
Step 1: m = grams q= Joules Δ T= ° C = 150° C c = x 2. Plug into equation: J= (15.75 grams)(x) ( 150° C) = x (specific heat capacity) c= .46 Joules

3. Do-now Solutions # 2
Step 1: List out your variables m= 10.0 grams c= .90 J/g.C Δ T = 55° C -22° C = 33 ° C q= unknown Step 2: Plug into equation q= mcΔt q= (10.0 grams)( .90 J) (33° C ) grams ° C q= 297 Joules

4. Step 1: List out your variables m= 50. 0 grams q= 5275 Joules c=
Step 1: List out your variables m= 50.0 grams q= 5275 Joules c= .50 Joules/grams. ° C Initial Temp: 20 ° C Final Temp: X ( unknown) Δ T: Final Temperature- Initial temperature: X-20° C Step 2: Plug in: q= m cΔ T 5275 Joules = (50.0 grams) (.50 Joules/ grams. ° C )(x-20° C ) 5275 J = (25 grams. Joules)(x-20° C ) ( grams. ° C) 5275 J = 25x J = 25 x ° C = X ( initial temperature)

5. Energy is absorbed
Energy is released

6. Vocab Potential Energy- stored energy
Kinetic Energy- energy having to do with motion
Heat of Fusion- the amount of heat needed to change solid to liquid at constant temperature
Heat of Vaporization- the amount of heat needed to change liquid to gas at constant temperature

7. 5 4 3 2
q=mHv 1
q=mHf

8. 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

9. Summary Melting and Freezing occur at the same temperature.
Vaporization and condensation occur at the same temperature.
During phase changes, the temperature remains constant (Plateau)
Questions
The heating curve shows an endothermic process, why?
The cooling curve shows an exothermic process, why?
Which two phases are present during melting/ freezing?
Vaporization/ condensation?