R1.4 Entropy and spontaneity
14 revision questions with answers for R1.4 Entropy and spontaneity, marked HL. Read them here, or play the set as a class game on the projector. Free to host, and students join with a code.
Measure of the dispersal of energy and matter in a system?
- Enthalpy
- Gibbs energy
- EntropyRight answer
- Activation energy
What this set covers
Entropy and spontaneity at HL: dispersal of energy and matter, standard entropy changes with state, ΔG = ΔH − TΔS, and how the signs of ΔH and ΔS decide the temperatures at which a reaction is spontaneous.
- Common mix-up
- Students often forget to convert units in ΔG calculations: ΔS is given in J K⁻¹ mol⁻¹ but ΔH is in kJ mol⁻¹, so they must match before you multiply by T.
- Revision tip
- Fill in a two-by-two table of ΔH and ΔS signs against spontaneity at low and high temperature, then test it on the 500 K question.
All 14 questions and answers
Measure of the dispersal of energy and matter in a system?
Answer: Entropy
Units of standard entropy, S⦵?
Answer: J K⁻¹ mol⁻¹
State of a substance with the highest entropy?
Answer: Gas
Which change gives the largest increase in entropy?
Answer: H₂O(l) → H₂O(g)
Sign of ΔS for CaCO₃(s) → CaO(s) + CO₂(g)?
Answer: Positive
Expression for ΔS⦵ from standard entropies?
Answer: ΣS⦵(products) − ΣS⦵(reactants)
For a spontaneous process, the total entropy of the universe…?
Answer: Increases
Equation for the Gibbs energy change?
Answer: ΔG = ΔH − TΔS
Sign of ΔG for a spontaneous reaction?
Answer: Negative
Value of ΔG for a reaction mixture at equilibrium?
Answer: Zero
A reaction with ΔH < 0 and ΔS > 0 is spontaneous…?
Answer: At all temperatures
A reaction with ΔH > 0 and ΔS > 0 becomes spontaneous…?
Answer: At high temperature
ΔH = +100 kJ mol⁻¹, ΔS = +200 J K⁻¹ mol⁻¹. Temperature above which it is spontaneous?
Answer: 500 K
ΔG at 300 K when ΔH = −50 kJ mol⁻¹ and ΔS = −100 J K⁻¹ mol⁻¹?
Answer: −20 kJ mol⁻¹
Play it as a class game
Play this set opens it in splycr, where you can host it for your class straight away. Hosting needs no account: put the room code on the projector, and students join from a phone with the code and their first name. Each question plays as multiple choice, and the three wrong options were written for that question.