Question 1: Solid ammonium nitrate, NH₄NO₃ (s), is a crystalline salt commonly used in commercial instant coldpacks, since it gives a highly endothermic heat of dissolution in water (ΔH_soln = +26.4 kJ/mol).

a. If 750 g of NH₄NO₃ (s) is mixed with 600 cm³ of water inside a cold-pack plastic sachet bag, what is the total amount of heat (in kJ) required by the dissolution process?

b. If density of water is 1 g/cm³ and assume that specific heat capacity of ammonium nitrate solution is very close to that of water (4.18 J/g·K), determine the final temperature of the pack (in ^oC) from an initial temperature of 25^oC. Specific heat capacity of plastic sachet is neglected.

Question 2: Conversion of elemental carbons, C(graphite) to C(diamond) at 25^oC, 1 atm is known to be a nonspontaneous process.

a. If ΔH_f^o of diamond is 1.895 kJ/mol, and S^o for graphite and diamond are 5.740 J/K·mol and 2.377 J/K·mol, respectively, calculate ΔH^o and ΔS^o for the conversion process.

b. By calculating ΔG^o, confirm that the expected conversion is really a non-spontaneous process at 25^oC.

Question 3: Ozone (O₃) is a gas which can be found in the outer layer of the earth atmosphere. This gas filter out the dangerous ultra violet light from the sun. Suppose that ozone is formed from oxygen via the reaction:

3O₂(g) → 2O₃ (g)

a. Determine the enthalpy change of the reaction.

b. Based only on the molecular order predict whether the entropy change of the reaction will increase or decrease. Confirm your answer by calculation if it is known that standard molar entropy of oxygen and ozone in the standard gaseous state are 205.138 and 238.930 J/K·mol, respectively.

c. If the standard enthalpy of formation for ozone gas is +142.70 kJ/mol, predict the spontaneity of the reaction at T = 600 K. Explain your answer.

Question 4: Jan 2014 Calculate ΔHo for the combustion of butane gas (C4H10), to produce gaseous carbon dioxide and liquid water:

2C₄H₁₀ (g) + 13O₂ (g) → 8CO₂ (g) + 10H₂O (l)

a. Calculate the standard enthalpy change, ΔH^o for the reaction.

b. Calculate the standard entropy change, ΔS^o for the reaction.

c. Determine whether the reaction is spontaneous at 25^oC.

Question 5: A cylinder with a movable piston contains 1 g of butane, C₄H₁₀ and excess oxygen. The cylinder is perfectly heat-conducting, therefore heat can be transferred to the surroundings with heat loss. A spark initiates combustion of the butane gas to form carbon dioxide and water vapour.

a. Write the equation to represent the internal energy change of the system in terms of heat and work. Identify the signs (positive or negative) for heat and work.

b. Write the thermochemical equations for the formation reactions of C₄H₁₀(g), CO2 (g) and H₂O(g).

c. Using Hess's law and the formation reactions in part(b), write the balanced equation for the combustion of butane.

d. Calculate the standard enthalpy for the combustion of butane, ΔH^o_rxn.