WJEC A Level Chemistry
WJEC A Level Chemistry 3.7 Entropy and Feasibility of Reactions Exam Questions
Free WJEC A Level Chemistry exam questions on 3.7 Entropy and Feasibility of Reactions, with mark schemes. Covers entropy, Gibbs free energy and feasibility.
3.7 Entropy and Feasibility of Reactions exam questions
1 question pack of real past exam questions with its mark scheme. Answer every question without notes, then mark your answers line by line against the mark scheme.
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WJEC A Level Chemistry Flashcards (Anki & Quizlet)
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Use them on Anki or Quizlet, then test yourself with the questions on this page.
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About WJEC A Level Chemistry 3.7 Entropy and Feasibility of Reactions
This topic explains why reactions happen.
What you need to know
- Entropy A measure of disorder; gases have higher entropy than liquids and solids.
- Entropy change ΔS = ΣS(products) − ΣS(reactants).
- Gibbs free energy ΔG = ΔH − TΔS; a reaction is feasible when ΔG ≤ 0.
- Temperature Find the temperature at which a reaction becomes feasible.
Common mistakes in 3.7 Entropy and Feasibility of Reactions
- Forgetting to convert ΔS from J to kJ.
- Saying feasible reactions always occur quickly.
- Getting the sign of ΔS wrong for gas production.
Try three 3.7 Entropy and Feasibility of Reactions exam-style questions
1. Calculate ΔG at 298 K if ΔH = +50 kJ mol⁻¹ and ΔS = +200 J K⁻¹ mol⁻¹. (2 marks)
Show the mark scheme answer
ΔG = 50 − 298 x 0.200 (1) = −9.6 kJ mol⁻¹ (1).
2. Explain why ΔS is positive for CaCO₃ → CaO + CO₂. (1 mark)
Show the mark scheme answer
A gas is formed from a solid, increasing disorder.
3. State the condition for feasibility. (1 mark)
Show the mark scheme answer
ΔG ≤ 0.
3.7 Entropy and Feasibility of Reactions FAQs
What does Entropy and Feasibility cover?
Entropy, Gibbs free energy and predicting feasibility.
What units are used?
ΔH in kJ mol⁻¹, ΔS in J K⁻¹ mol⁻¹, so convert before combining.
Can kinetics stop a feasible reaction?
Yes, if the activation energy is high.
Revise this topic with flashcards: WJEC A Level Chemistry Flashcards, with mark scheme answers for Anki and Quizlet.
