A-Level CIE Chemistry 5.1 Thermodynamics (A Level only): 3 (a) Explain what is meant by t

Question

3 (a) Explain what is meant by the term entropy of a system.

Entropy is a measure of the disorder or randomness of a system.

(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
The entropy change is negative because cooling a substance decreases its molecular motion and thus the disorder.

- solid calcium chloride is added to water and the mixture is stirred
The entropy change is positive because solid calcium chloride dissociates into an aqueous solution, increasing disorder.

- the change corresponding to the lattice energy of calcium chloride, ΔH_lat CaCl₂(s), takes place
The entropy change is negative because gas ions become solid, resulting in decreased disorder.

(c) The reaction ZnCO₃(s) → ZnO(s) + CO₂(g) is not spontaneous at room temperature.

(i) Give the full name for the term ΔG*.
ΔG* is the standard Gibbs free energy change.

(ii) Describe how the temperature at which the reaction becomes spontaneous can be calculated. Include an equation in your answer.
The temperature can be calculated using the equation ΔG = ΔH - TΔS, where at the spontaneous point ΔG = 0.

3 (a) Explain what is meant by the term entropy of a system - CIE - A-Level Chemistry - Question 3 - 2019 - Paper 1

Worked Solution & Example Answer:3 (a) Explain what is meant by the term entropy of a system - CIE - A-Level Chemistry - Question 3 - 2019 - Paper 1

Explain what is meant by the term entropy of a system.

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, ΔH_lat CaCl₂(s), takes place

Give the full name for the term ΔG*.

Describe how the temperature at which the reaction becomes spontaneous can be calculated. Include an equation in your answer.

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