Lon-Capa 5 th HW assignment due Friday by 5 pm. 4 th Quiz due Sunday, 10/25 by 10 pm. It will open Friday at 5 pm. (Exam 2 is Tuesday, October 27) 1

2 Clicker Question Consider the spontaneous reaction: 2KClO 3 (s)  2KCl(s) + 3O 2 (g) Is the reaction endothermic or exothermic? a) Endothermic b) Exothermic c) More information is needed. d) I do not know how to answer this question.

3 The meaning of  G rxn At constant temperature and pressure the sign indicates the spontaneity of the reaction.  G rxn < 0 means spontaneous  G rxn > 0 means not spontaneous (or spontaneous in the opposite direction) If we change the temperature we can change the sign of  G rxn The magnitude of  G rxn tells us the relative extent of the reaction (recall that K does too!) If we change the temperature we can change the magnitude of  G rxn.

4 Determining  G  rxn Consider the following reaction at constant temperature and pressure: 2CO(g) + O 2 (g)  2CO 2 (g) Consider: 1. Predict if  S° is positive or negative (we will determine it next). 2. Predict if the reaction is exothermic or endothermic (we will determine it next). 3. Can we predict the sign of  G°? 4. At what temperatures is this reaction spontaneous?

5 Determining  G  rxn 2CO(g) + O 2 (g)  2CO 2 (g)  G  (kJ/mol)  H  (kJ/mol) S  (J/Kmol) Consider: 1. Determine  S° (check prediction). 2. Determine  H° (check prediction). 3. Determine  G° two ways. 4. At what temperatures is this reaction spontaneous?

6 Recall: Questions To Consider Why do systems reach equilibrium? That is, why doesn’t the ball go all the way down the hill?