1. Representing Enthalpy Change 1

2.  I will be able to use proper scientific terminology to describe  I will be able to use various methods to represent enthalpy changes 2

3.  define the terms: thermochemical equation, potential energy diagram  represent enthalpy changes using thermochemical equations with energy terms, thermochemical equations with ΔH values, molar enthalpies of reaction and potential energy diagrams 3

4. When a reaction is endothermic, energy is absorbed (consumed) and is always represented on the reactant side of the yield arrow H 2 O (l) + 285.8 kJ  H 2(g) + 1/2 O 2(g) When a reaction is exothermic, energy is released (produced) and is always represented on the product side of the yield arrow Mg (s) + 1/2 O 2(g)  MgO (s) + 601.6 kJ 4

5. Write a balanced chemical equation and then the ∆H value beside it (∆H is negative when exothermic and positive when endothermic) CO (g) + 2H 2(g)  CH 3 OH (l) ∆H = -128.6 kJ 5

6. Molar enthalpy of reaction, ∆H x the energy change associated with the reaction of one mole of a substance (also called molar enthalpy change) Molar enthalpy that is determined when initial and final conditions of the chemical system are at SATP (100 kPa and 25ºC) is called a standard molar enthalpy of reaction (∆Hº x ) Note: Difference between ∆H x and ∆Hº x 6

7. 7

8. The symbol for the molar enthalpy of reaction uses the subscript “r” to refer to the reaction under consideration CO (g) + 2 H 2(g)  CH 3 OH (l) ∆Hº r = -128.6 kJ/mol CH 3 OH 8

9.  Chemical potential energy is the stored energy related to the relative positions of particles and the strengths of the bonds between them  PE is stored or released as the positions of the particles change  As bonds break and re-form and the positions of atoms are altered, changes occur in PE  Potential energy diagrams are graphical representations of the energy transferred during a physical or chemical change 9

10.  Vertical axis represents the potential energy of system  Horizontal axis represents the reaction coordinate or reaction progress  Reactants are written on the left and the products on the right 10

11. 11

12. 12

13. 13

14. 14

15. 15 Practice pp. 319-320 UC # 1, 2, 3, 4, 5 Section 5.3 Questions p. 320 UC # 1, 2, 3