P1) A liquid sample that weighs 2.585 g is a mixture of butane (C4H10) and hexane (C6H14). When the sample is combusted in an excess of oxygen, 3.929 g of water are formed. a. How much butane and hexane (answer in g) were in the original sample? b. How much CO2 (answer in g) was produced in the combustion of the sample?

P2) The compound acrylonitrile can be made in the following reaction: 2C3H6(g) + 2NH3(g) + 3O2(g) ? 2C3H3N(g) + 6H2O(g) A 250.0 L reaction vessel is charged to the following partial pressures at 500°C: PC3H6 = 10.0 atm PNH3 = 12.0 atm PO2 = 9.0 atm

a. What is the total pressure in the vessel just after the reagent gases are added (assume ideal behavior)?

b. What are the mole ratios of the reagent gases in the vessel before the reaction begins?

c. What is the total pressure in the chamber after the reaction has gone to completion (i.e. all of at least one of the reactants is used up)?

d. What is the partial pressure of acrylonitrile in the vessel after the reaction has gone to completion? e. What mass of acrylonitrile is produced after the reaction has gone to completion?

P3) The manager of a small chemical plant receives an order for 2000 kg, of a 30% solution (by weight) of phosphoric acid in water (this is used as a food additive for cattle; it boosts milk production). The solution is prepared at the plant just prior to delivery by reacting solid calcium phosphate with concentrated sulfuric acid (which is 2% water by weight) to make the phosphoric acid, which is then added to water to make the final solution.

The other product of the reaction, calcium sulfate, is dried and sold as a soil additive.

a. What are the molecular weights of H3PO4, H2SO4, Ca3(PO4)2 and CaSO4?

b. What is the balanced chemical equation for the reaction used to produce phosphoric acid?

c. What mass (or weight) of concentrated sulfuric acid will be required in the reaction to produce the amount of phosphoric acid solution that was ordered? P4) Consider a simple cylinder and piston used to perform experiments on gases. The trapped volume under the piston contains 4.65 g of argon gas. Assume the Ar to be ideal in answering parts a-d below. For part e, assume the Ar obeys a van der Waals equation of state.

a. When the pressure applied by the piston on the gas is 0.951 atm at a temperature of 25.0°C, what is the trapped volume of the Ar?

b. If the pressure on the cylinder is increased to 5.30 atm and the temperature is maintained constant, what will be the new volume of the gas? 4

c. Keeping the pressure constant at 5.30 atm, the gas is heated until the total volume of the gas is 2.00

L. What is the temperature of the gas? d. The gas is cooled back to 25.0°C and at the same time the pressure is decreased. The volume is now measured to be 4.48L. What is the pressure of the gas?

e. Repeat the calculation for part d but now assume that the Ar gas obeys the van der Waals equation of state: [P + a(n/V)2](V - nb) = nRT with a = 1.35 atm L2 mol-2 and b = 0.0322 L mol-1. P5)

Use Hess's Law to calculate the enthalpy of formation of tetraborane. B4H10(g), from the following enthalpies of combustion: 2B(S) + 3/2 O2(g) ? B2O3(S) ?Hrxn(1) = -1255.0 kJ H2(g) + ½ O2(g) ? H2O (liq) ?Hrxn(2) = -286.0 kJ B4H10(g) +11/2 O2(g) ? 2 B2O3(s) + 5 H2O(liq) ?Hrxn(3) = -4010.0 kJ P6)

The equilibrium constant for the ammonia synthesis reaction, N2(g) + 3 H2(g) ? 2NH3(g), is Kp = 0.10 atm-2 @ 500K.

a. Write the expression for the equilibrium constant in terms of the partial pressures of the gaseous reactants and products.

b. Consider a reactor at 500K. If the partial pressures of N2 and H2 are maintained at 1 atm and 3 atm, respectively, what is the partial pressure of NH3 in the reactor?

c. The ammonia reaction as written above is exothermic. What happens to the equilibrium constant when the temperature of the reactor is increased?

d. If the ratio of the N2 and H2 partial pressures is maintained at 1:3, what total pressure in the reactor is necessary to achieve a 1 atm partial pressure of ammonia at 500K?

e. Make a sketch of the partial pressure of ammonia in the reactor as a function of time if the volume of the reactor is suddenly doubled, and the gas mixture returns to equilibrium at constant temperature. P7)

A constant volume container holds an equilibrium mixture of Cl2(g), PCl3(g), and PCl5(g) gases, which have partial pressures of 2.7, 2.7, and 9.1 torr, respectively. An amount of Cl2(g) is quickly injected into the container until the total pressure reaches 20 torr, and then the total pressure in the container is measured as the system relaxes back to equilibrium. Answer the following questions about this system:

a. What is the balanced chemical reaction for this equilibrium system and the numerical value of the corresponding equilibrium constant?

b. Sketch a diagram of the total pressure in the container as a function of time, starting before the additional Cl2(g) was injected until equilibrium is again achieved.

c. Sketch a diagram showing the partial pressures of Cl2(g) and PCl3(g) as functions of time.

5 d. Calculate the partial pressures of the three gases after the system has relaxed back to equilibrium. Selected Answers: 1a: Grams(butane) = 1.52gr. Grams(hexane) = 1.03gr. 3: 919.2 kg of H2SO4 5: 70kJ. 6b: 1.64 atm 7b: 18.55 torr