1. Unit 5: Thermochemistry
Specific Heat

2. Thermochemistry
thermochemistry: studies the relationships between chemical reactions and energy changes involving heat

3. Thermochemistry Heat and temperature are NOT the same thing!
Temperature: a measure of the random motions of molecules (average kinetic energy)
Heat: transfer/flow of energy due to a temperature difference (from high to low)

4. Specific Heat
specific heat: willingness of an object to change temperature, with the symbol Cp (the p means "under constant pressure")
specific heat: the amount of energy required to change the temperature of one gram of a substance by 1°C

5. Specific Heat Units
1 calorie = energy required to heat 1 gram of water by 1°C
1 Calorie (food labels) = 1 kilocalorie
1 calorie = joules

6. Specific Heat
Duluth, next to Lake Superior, stays cool in the summer and relatively warm in the winter. Why? (Hint: heat is a willingness to change temperature.)
Substance
Specific Heat (J/g°C)
granite
0.7953
lead
0.1276
ice
2.06
water
4.184

7. Calculating Heat (Energy Transfer)
q = Cp x m x T
change in temperature
(units: °C)
heat
(units: J or cal)
specific heat (units: J/g°C)
mass
(units: g)

8. Calculating Heat Example
q = Cp x m x T
3.05 kg of aluminum is heated from 22.1C to 67.5C. Calculate the heat absorbed in both J and kJ by the metal. The specific heat of aluminum is J/gC.

9. Calculating Heat – Practice WS #4
q = Cp x m x T
If g of water at 20.0C absorbs J of heat, what will the final temperature of the water be?