Reference no: EM13834414
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 (ΔHsoln = +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 25oC. Specific heat capacity of plastic sachet is neglected.
Question 2: Conversion of elemental carbons, C(graphite) to C(diamond) at 25oC, 1 atm is known to be a nonspontaneous process.
a. If ΔHfo of diamond is 1.895 kJ/mol, and So for graphite and diamond are 5.740 J/K·mol and 2.377 J/K·mol, respectively, calculate ΔHo and ΔSo for the conversion process.
b. By calculating ΔGo, confirm that the expected conversion is really a non-spontaneous process at 25oC.
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, ΔHo for the reaction.
b. Calculate the standard entropy change, ΔSo for the reaction.
c. Determine whether the reaction is spontaneous at 25oC.
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, ΔHorxn.
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