1. 16.1 Thermochemistry

2. POINT > Define temperature and heat POINT > Define specific heat POINT > Describe enthalpy of reaction POINT > Define enthalpy of formation POINT > Define enthalpy of combustion

3. POINT > Define temperature and heat Temperature is a measure of the average kinetic energy of the particles in a substance Heat is the flow of thermal energy from a substance with higher temperature to one with lower temperature Energy transferred as heat is measured in Joules (J)

4. POINT > Define specific heat Specific heat (c p ) is the energy required to raise the temperature of 1 gram of a substance 1°K (or °C) c p of water = 4.18 J/g°K (= 1 calorie) c p of lead = 0.13 J/g°K

5. POINT > Define specific heat Specific heat (c p ) can be related to energy lost or gained by a substance with the equation: q = c p x m x ΔT q = Joules m = mass ΔT = temperature change

6. WB CHECK: q = c p x m x ΔT 88.4 J was required to raise the temperature of 10.0 g of a substance from 215.0 °K to 230 °K. What is the specific heat of the substance? c p = 0.589 J/ g °K

7. WB CHECK: q = c p x m x ΔT How much energy would be required to raise the temperature of this substance another 55 °K? 324 joules

8. POINT > Describe enthalpy of reaction Heat is transferred during virtually all chemical reactions H represents a quantity called enthalpy (not directly measurable) ∆H is the change in enthalpy in a reaction: ∆H = H products - H reactants = Enthalpy of Reaction

9. POINT > Describe enthalpy of reaction ∆H = H products - H reactants We can measure this energy change in a calorimeter Enthalpy of Reaction

10. POINT > Describe enthalpy of reaction The energy change during the reaction is measured by the change in temperature of the water

11. WB CHECK: What is a calorimeter used for? Suppose a calorimeter contains 100.0ml of water. A reaction raises the temperature of the water by 10 °C. How much energy was released by the reaction? 4180 J

12. POINT > Describe enthalpy of reaction ∆H = H products - H reactants Endothermic reactions: the products have more energy than the reactants and ∆H is positive Energy is absorbed from the surroundings. This reaction flask would feel cool/cold

13. POINT > Describe enthalpy of reaction ∆H = H products - H reactants

14. POINT > Describe enthalpy of reaction ∆H = H products - H reactants Exothermic reactions: the reactants have more energy than the products and ∆H is negative. Energy is released to the surroundings. This reaction flask would feel warm/hot Products of exothermic reactions tend to be very stable

15. POINT > Describe enthalpy of reaction ∆H = H products - H reactants.

16. WB CHECK: What is an endothermic reaction? What is an exothermic reaction?

17. POINT > Describe enthalpy of reaction A thermochemical equation includes ∆H 2CO(g) + O 2 (g)  2CO 2 (g)  H = -566.0 kJ (exothermic) 2H 2 O(g)  2H 2 (g) + O 2 (g)  H = 483.6 kJ (endothermic) 2H 2 (g) + O 2 (g)  2H 2 O (g)  H = -483.6 kJ (exothermic) Thermochemical equations must include the physical state of reactants/products

18. POINT > Define enthalpy of formation The enthalpy of formation ∆H ◦ f is the energy change when one mole of a compound is formed from its elements All reactants are in standard state 2H 2 (g) + O 2 (g)  2H 2 O (l)  H = -571.6J ∆H ◦ f = -285.8J Appendix B-14 gives ∆H ◦ f for a variety of common compounds (p R66)

19. POINT > Define enthalpy of formation The enthalpy of formation ∆H ◦ f is the energy change when one mole of a compound is formed from its elements. All reactants are in standard state Compounds with exothermic enthalpy of formation tend to be very stable Appendix B-14 gives ∆H ◦ f for a variety of common compounds (p R66)

20. POINT > Define enthalpy of combustion The enthalpy of combustion ∆H c is the energy change when one mole of a compound is combusted CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O (l)  H = -891 kJ Appendix B-5 gives ∆H c for a variety of common compounds (p. R60)

21. WB CHECK: What is enthalpy of formation? What is enthalpy of combustion?

22. WB CHECK: Does this energy diagram show an exothermic or endothermic reaction?

23. Homework: Read Section 16.1 Pages 501-509 Section Assessment Page 514 #1-3, 5 Continue pH and titration calculation practice