AgNO 3 + HCl  When 50.0 mL of M AgNO 3 and 50.0 mL of M HCl are mixed in a coffee-cup calorimeter, the mixture’s temperature increases from o C to o C. Calculate the enthalpy change for the reaction, per mole of AgNO 3. AgCl + HNO L, 0.1 M 0.05 L, 0.1 M mol Assume: -- mixture mass = 100 g -- mixture c P = c P of H 2 O q = m c P  T = 100 (4.18) (23.11–22.30) = J (for mol AgNO 3 ) –  H = J mol AgNO kJ mol AgNO 3

Combustion reactions are studied using constant- volume calorimetry. This technique requires a bomb calorimeter. -- The heat capacity of the bomb calorimeter (C cal ) must be known. bomb calorimeter unit is J/K (or the equivalent)

another bomb calorimeter -- Again, we assume that no energy escapes into the surroundings, so that the heat absorbed by the bomb calorimeter equals the heat given off by the reaction. Solve bomb calorimeter problems by unit cancellation.

A g sample of propane, C 3 H 8, is burned in a bomb calorimeter with a heat capacity of 3.75 kJ/ o C. The temperature of the material in the calorimeter increases from o C to o C. Calculate the molar heat of combustion of propane. –2220 kJ/mol (27.83 o C–23.22 o C) kJ g 3.75 kJ o C

Hess’s Law The  H rxn s have been calculated and tabulated for many basic reactions. Hess’s law allows us to put these simple reactions together like puzzle pieces such that they add up to a more complicated reaction that we are interested in. By adding or subtracting the  H rxn s as appropriate, we can determine the  H rxn of the more complicated reaction. The area of a composite shape can be found by adding/subtracting the areas of simpler shapes.

8 O 2 (g) Calculate the heat of reaction for the combustion of sulfur to form sulfur dioxide. 2 SO 2 (g) + O 2 (g)2 SO 3 (g)(  H = –198.2 kJ) S 8 (s) + 12 O 2 (g)8 SO 3 (g)(  H = – kJ) S 8 (s) + 8 O 2 (g) 8 SO 2 (g) S 8 (s) + 12 O 2 (g)8 SO 3 (g) (  H = – kJ) (TARGET) 2 SO 3 (g) 2 SO 2 (g) + O 2 (g) (  H = kJ) need to cancel… S 8 (s)+8 SO 2 (g)  H = – kJ 8 SO 3 (g) 8 SO 2 (g) + 4 O 2 (g) (  H = kJ) 2 SO 2 (g) + O 2 (g)2 SO 3 (g) (  H = –198.2 kJ)

Calculate  H for the reaction… 5 C + 6 H 2 C 5 H 12 given the following: C 5 H O 2 5 CO H 2 O (  H = – kJ) C + O 2 CO 2 (  H = –393.5 kJ) H 2 + ½ O 2 H 2 O (  H = –285.8 kJ) C 5 H O 2 5 CO H 2 O (  H = – kJ) 5 CO H 2 O C 5 H O 2 (  H = kJ) C + O 2 CO 2 (  H = –393.5 kJ) 5 C + 5 O 2 5 CO 2 (  H = – kJ) H 2 + ½ O 2 H 2 O (  H = –285.8 kJ) 6 H O 2 6 H 2 O (  H = – kJ) 5 C+ 6 H 2 C 5 H 12  H = –146.7 kJ

Calculate  H for the reaction… 5 C + 6 H 2 C 5 H 12 given the following: C 5 H O 2 5 CO H 2 O (  H = – kJ) C + O 2 CO 2 (  H = –393.5 kJ) H 2 + ½ O 2 H 2 O (  H = –285.8 kJ) C 5 H O 2 5 CO H 2 O kJ5 CO H 2 O kJC 5 H O 2 C + O 2 CO kJ 5 C + 5 O 2 5 CO kJ H 2 + ½ O 2 H 2 O kJ 6 H O 2 6 H 2 O kJ 5 C+ 6 H 2 C 5 H kJ  H = –146.7 kJ