Chapter 6 Review. Part 1: Change in Internal Energy

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Ethelbert Berry
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1 Chapter 6 Review This is my own personal review, this should not be the only thing used to study. You should also study using notes, PowerPoint, homework, ect. I have not seen the exam, so I cannot say for certain what is going to be on the exam. Part 1: Change in Internal Energy 1. The internal energy of a system increased by 982 J when it absorbed 492 J of heat. Was work done by or on the system? How much work was done? What is ΔV if pressure is constant at 1 atm? 2. A gas in a cylinder was placed in a heater and gained 5500 kj of heat. If the cylinder increased in volume from 345 ml to 1846 ml against an atmospheric pressure of 750 Torr during the process, what is the change in internal energy of the gas in the cylinder? 3. The change in internal energy for the combustion of 1.00 mol CH4(g) in a cylinder according to the reaction CH4(g) + 2 O2(g) CO2 (g) + 2 H20(g) is kj. If a piston connected to the cylinder performs 492 kj of expansion work due to the combustion, how much heat is lost from the system? What is this system in this situation?

2 Part 2: Heat Problems 1. How much energy is needed to change the temperature of 50.0 g of water by 15.0 o C? 2. How many grams of water can be heated from 20.0 o C to 75 o C using Joules? 3. What is the final temperature after 840 Joules is absorbed by 10.0g of water at 25.0 o C? 4. The heat capacity of aluminum is J/g o C. a. How much energy is needed to raise the temperature of a 8.50 x 10 2 g block of aluminum from 22.8 o C to 94.6 o C?

3 Part 3: Coffee Cup Calorimetry 1. A piece of metal weighing g was heated to C and then put it into ml of water (initially at 23.7 C). The metal and water were allowed to come to an equilibrium temperature, determined to be 27.8 C. Assuming no heat lost to the environment, calculate the specific heat of the metal. 2. In a coffee-cup calorimeter, g of H 2 O and ml of HCl are mixed. The HCl had an initial temperature of 44.6 o C and the water was originally at 24.6 o C. After the reaction, the temperature of both substances is 31.3 o C. A. Was the reaction exothermic or endothermic? Explain. B. Calculate how much heat the water lost or gained.

4 Part 4: Bomb Calorimetry 1. A g sample of octane (C8H18) is burned in a bomb calorimeter containing 1200 grams of water at an initial temperature of o C. After the reaction, the final temperature of the water is o C. The heat capacity of the calorimeter (also known as the calorimeter constant ) is 837 J/ o C. The specific heat of water is J/g o C. Calculate the molar heat of combustion of octane. 2. A1.000gramsampleoftherocketfuelhydrazine(N2H4) is burned in a bomb calorimeter. The temperature rises from C to C. The heat capacity of the calorimeter (including the water) is 5860 J/ C. Calculate the molar heat of combustion of hydrazine, in kj/mole. 3. A 0.500g sample of TNT (C7H5N2O6) is burned in a bomb calorimeter containing 610 grams of water at an initial temperature of o C. The heat capacity of the calorimeter is 420 J/ o C and the heat of combustion of TNT is 3374 kj/mol. Using these data, calculate the final temperature of the water and calorimeter once the reaction is complete.

5 Part 5: Hess Law 1. Calculate DH for the reaction: C2H4 (g) + H2 (g) --> C2H6 (g), from the following Data. C2H4 (g) + 3 O2 (g) --> 2 CO2 (g) + 2 H2O (l) C2H6 (g) + 3½ O2 (g) --> 2 CO2 (g) + 3 H2O (l) H2 (g) + ½ O2 (g) --> H2O (l) DH = kj DH = kj DH = kj 2. Calculate DH for the reaction 4 NH3 (g) + 5 O2 (g) --> 4 NO (g) + 6 H2O (g), from the following Data. N2 (g) + O2 (g) --> 2 NO (g) N2 (g) + 3 H2 (g) --> 2 NH3 (g) DH = kj DH = kj 2 H2 (g) + O2 (g) --> 2 H2O (g) DH = kj

6 3. Calculate DH for the reaction CH4 (g) + NH3 (g) --> HCN (g) + 3 H2 (g), given: N2 (g) + 3 H2 (g) --> 2 NH3 (g) C (s) + 2 H2 (g) --> CH4 (g) H2 (g) + 2 C (s) + N2 (g) --> 2 HCN (g) DH = kj DH = kj DH = kj

7 Part 6: Delta H of Formation/ Reaction 1. NaOH(s) + HCl(g) ----> NaCl(s) + H2O(g) 2. 2 CO(g) + O2(g) ---> 2 CO2(g) 3. CH4(g) + 2 O2(g) ---> CO2(g) + 2 H2O(l) 4. 2 H2S(g) + 3 O2(g) ---> 2 H2O(l) + 2 SO2(g) Compound DH f (kj/mol) Compound H f (kj/mol) CH 4(g) HCl(g) CO 2(g) H 2O(g) NaCl(s) SO 2(g) H 2O(l) NH 4Cl(s) H 2S(g) NO(g) H 2SO 4(l) NO 2(g) MgSO 4(s) SnCl 4(l) MnO(s) SnO(s) MnO 2(s) SnO 2(s) NaCl(s) SO 2(g) NaF(s) SO 3(g) NaOH(s) ZnO(s) NH 3(g) ZnS(s)

CHEM 1105 S10 March 11 & 14, 2014

CHEM 1105 S10 March 11 & 14, 2014 Today s topics: Thermochemistry (Chapter 6) Basic definitions Calorimetry Enthalpy Thermochemical equations Calculating heats of reaction Hess s Law Energy and Heat Some