1. THERMOCHEMISTRYTHERMOCHEMISTRY Chapter 11

2. HEAT CAPACITY AND SPECIFIC HEAT The amount of energy needed to to increase the temperature of an object exactly 1 0 C is the heat capacity of that object. (J/ 0 C) The specific heat capacity or simply specific heat of a substance is the amount of heat/ energy needed to raise the temperature of 1g of the substance 1 0 C. (J/g 0 C)

3. Calculating Heat Capacity The heat capacity of an object is equal to its specific heat times its mass. EX. The heat capacity of a 5 gram piece of pure aluminum is equal to: 5g X 0.90J/g 0 C = 4.50 J/ 0 C

4. Calculating Specific Heat C = __q___ = m X ΔT = heat(joules or calories) mass(g) X change in temperature ( 0 C)

5. Sample Problem How much heat is required to raise the temperature of 250 g of mercury 52 0 C? The specific heat for mercury is: 0.14 J/g 0 C

6. SOLVE for q(heat) C = __q___ m X ΔT Rearrange the specific heat formula to solve for q. q = C x m x ΔT NOW PLUG AND CHUG…

7. ANSWER q = C x m x ΔT q = 0.14 J x 250g x 52 0 C = g 0 C = 1,800 J or 1.8kJ

8. CALORIMETRY Calorimetry is the accurate and precise measurement of heat change for chemical and physical processes. In calorimetry, the heat released by the system is equal to to the heat absorbed by its surroundings. What law describes this relationship?

9. Calorimeter To measure heat changes accurately and precisely, the process must be carried out in an insulated container. The insulated device used to measure the absorption or release of heat in chemical or physical processes is called a calorimeter.

10. Heat of Reaction A heat of reaction is the heat change for the equation exactly as it is written. For systems at constant pressure, the heat content is the same as a property called the Enthalpy (H) of the system. (q = ΔH)

11. Thermochemical Equations You can treat heat change in a chemical reaction like any other reactant product in a chemical equation. A chemical equation that includes the heat change is referred to as a thermochemical equation.

12. ΔH is Positive

13. ΔH is Negative

14. Types of Thermochemical Equations Endothermic (ΔH is positive): Na 2 CO 2 + H 2 O + CO 2 + 129kJ NaHCO 3 Exothermic (ΔH is negative): CaO + H 2 O Ca(OH) 2 + 65.2KJ