A-LevelChemistryChemical energetics9701/43 · Oct/Nov 2019 · Q37 Marks
Explain what is meant by the term entropy of a system.
- (a)Explain what is meant by the term entropy of a system.[1]
- (b)State and explain whether the entropy change of each of the following processes is positive or negative. Do not consider the entropy change of the surroundings. • liquid water at 80°C is cooled to 60°C • solid calcium chloride is added to water and the mixture is stirred • the change corresponding to the lattice energy of calcium chloride, ∆Hlatt CaCl₂(s), takes place[3]
- (c)(i)The reaction ZnCO3(s) → ZnO(s) + CO2(g) is not spontaneous at room temperature. Give the full name for the term ∆G°.[1]
- (c)(ii)Describe how the temperature at which the reaction becomes spontaneous can be calculated. Include an equation in your answer.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.
- [1] a measure / degree of disorder / randomness of a system
- [3] M1: negative – molecules have less energy in the system M2: positive – solid being converted into an aqueous solution M3: negative – gaseous ions being converted into a solid
- [1] (standard) Gibbs free energy change
- [2] M1: (Δ)G = ΔH−TΔS M2: description of calculating the minimum value of T for which ΔG is zero / becomes negative OR T = ΔH / ΔS [1]
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