1. Hydrazine (N2H4) is a fuel used by some spacecraft. It is normally oxidized by N2O4 according to the equation:
N2H4(l) + N2O4(g) → 2 N2O(g) + 2 H2O(g)
Calculate ΔrH°(in kJ mol-1) for this reaction using the information given:
ΔfH°[N2H4(l)] = 97.0 kJ mol-1
ΔfH°[N2O4(g)] = 7.1 kJ mol-1
ΔfH°[N2O(g)] = 83.2 kJ mol-1
ΔfH°[H2O(g)] = -250.0 kJ mol-1
2. How much heat (in joules) is required to raise the temperature of 83.0 grams of water by 3.0 °C?
3. Nitrogen gas, N2, can be prepared by passing gaseous ammonia, NH3, over solid copper(II) oxide, CuO, at high temperatures. The other products of the reaction are solid copper, Cu, and water vapour. In a certain experiment, a reaction mixture containing 16.1 g NH3 and 52.1 g CuO yields 1.7 g N2. Calculate the percent yield for this experiment
4. A piece of metal with Cs = 0.683 J/g0C and initial temperature of 5.80C is placed into 165.0 grams of water at 33.70C. If thermal equilibrium is reached at a temperature of 21.20C, what is the mass (in grams) of the metal? (For water, Cs = 4.184 J/g0C)
5. Two cubes (R and Q) with different initial temperatures are placed into direct contact, allowing transfer of thermal energy. If they have the same mass but the specific heat of Q is 10% greater than the specific heat of R, the final temperature when thermal equilibrium is reached will be:
options:
- closer to the initial temperature of R
- closer to the initial temperature of Q
- exactly midway between the initial temperatures of R and Q
- 10 times greater than the initial temperature of Q
- greater than the initial temperature of both R and Q
6. A system releases 8 kJ of heat and its internal energy change was -362 kJ. How much work (in kJ) did it do on the surroundings?
7. The dissolving of sodium acetate (NaC2H3O2 = 82.04 g/mol) in water can be described by the following:
NaC2H3O2 (s) à NaC2H3O2 (aq) DH = –17.2 kJ
How much heat (in kJ) will be released when 154.0 g of sodium acetate dissolve in water?
8. If the reaction below produces 7,360.0 kJ of energy, how many grams of KCl will be produced? (KCl = 74.6 g/mol)
2 K (s) + Cl2 (g) à 2 KCl (g) ΔHrxn = –873.0 kJ
9. In order to determine Ccal for a brand new calorimeter, a test reaction that is known to release 5.5 kJ of heat is carried out. The reaction causes a temperature increase of 2.8 oC. What is the heat capacity of the calorimeter (in kJ/oC)?
