EntropyAQA A-Level Chemistry: Flashcards

What these 13 flashcards ask

What is entropy?
What are the units of entropy?
Why is ΔH not sufficient to predict feasibility?
Put solid, liquid and gas in order of increasing entropy.
What is the sign of ΔS for melting?
What is the sign of ΔS for condensation?
What is the formula for the entropy change of a reaction?
How do you predict the sign of ΔS for a reaction?
Is ΔS positive or negative for N₂(g) + 3H₂(g) → 2NH₃(g)?
Why does dissolving a solid usually increase entropy?
What happens to the entropy of a substance when it is heated?
Why does a gas have much higher entropy than a liquid?
How do you use coefficients in entropy calculations?

Exam questions on Entropy

A student discusses entropy using the three physical states of water. She considers how the disorder of the particles in ice, liquid water and steam changes as a sample of water is heated from below 0 °C to above 100 °C at constant pressure.
Explain why the entropy of steam is greater than the entropy of liquid water at the same temperature.2 marks
Ammonia is made industrially in the Haber process: N₂(g) + 3H₂(g) → 2NH₃(g). Standard entropies (J K⁻¹ mol⁻¹): N₂(g) = 192; H₂(g) = 131; NH₃(g) = 193.
Predict, with a reason, the sign of the entropy change for the reaction Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g).2 marks
Calcium carbonate decomposes on strong heating: CaCO₃(s) → CaO(s) + CO₂(g), ΔH = +178 kJ mol⁻¹. Standard entropies (J K⁻¹ mol⁻¹): CaCO₃(s) = 93; CaO(s) = 40; CO₂(g) = 214. Relative formula mass of CaCO₃ = 100.1.
Calculate the entropy change for the decomposition of calcium carbonate. Include units.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).