Lon-Capa 4 th HW assignment due Friday, 10/9, 5 pm. It is open now. 3 rd Quiz due Sunday, 10/11 by 10 pm. It will open Friday, 10/9 at 5 pm. 5 th HW assignment is also open! 1

2 The Piston, Moving a Distance Against a Pressure P, Does Work On the Surroundings

3 Determining  H rxn Since  H = q p, determine the heat given off or required at constant pressure by measuring temperatures. This is termed calorimetry. Since energy is conserved, we can often determine  H rxn for one reaction given values of  H rxn for others. Uses the principle in Hess’s Law. Use standard enthalpies of formations for reactants and products (we have tables of these).

4 A Coffee- Cup Calorimeter Made of Two Styrofoam Cups

5 Specific Heat Capacities

6 Constant-Pressure Calorimetry Can determine enthalpy change for chemical reactions that occur in solution. See Example 9.3 on page 376 of your text. Can calculate ΔE and ΔH when PV work occurs. See Example 9.4 on page 378 of your text.

7 Bomb Calorimeter

8 Hess’s Law Due to first law and  H being a state function. If a reaction is reversed, the sign of  H is also reversed The magnitude of ΔH is directly proportional to the quantities of reactants and products in a reaction. That is, if the coefficients in a balanced equation are multiplied by an integer, the value of  H is multiplied by the same integer.

9 Clicker Question Given the following data 2NH 3 (g)  N 2 (g) + 3H 2 (g)  H = 92kJ 2H 2 (g) + O 2 (g)  2H 2 O(g)  H = -484kJ Determine ΔH for 2N 2 (g) + 6H 2 O(g)  3O 2 (g) + 4NH 3 (g) a) kJ b) 1268 kJ c) 1636 kJ d) kJ e) I did not/cannot get any of these answers.