Entropy and Gibbs Free Energy: Flashcards
Revise entropy, the second law, predicting ΔS, ΔG = ΔH − TΔS, the four sign cases and ΔG° = −RT ln K.
Entropy and Gibbs Free Energy: Flashcards
- QuestionWhat is entropy?Answer
A measure of how spread out energy and matter are (the number of possible arrangements). Unit of S°: J mol⁻¹ K⁻¹.
- QuestionState the second law of thermodynamics.Answer
In a spontaneous process, the total entropy of the universe increases.
- QuestionWhen is ΔS of a reaction positive?Answer
When moles of gas increase, a solid melts or a liquid boils, or (usually) a solid dissolves.
- QuestionGibbs free energy equation?Answer
ΔG = ΔH − TΔS, with T in kelvin and ΔS converted to kJ/K.
- QuestionWhat does the sign of ΔG tell you?Answer
Negative: spontaneous. Zero: at equilibrium. Positive: not spontaneous (the reverse is).
- QuestionΔH negative and ΔS positive?Answer
ΔG is negative at all temperatures: always spontaneous.
- QuestionΔH positive and ΔS positive?Answer
Spontaneous only at high temperature, above T = ΔH ÷ ΔS (e.g. CaCO₃ → CaO + CO₂).
- QuestionΔH negative and ΔS negative?Answer
Spontaneous only at low temperature, below T = ΔH ÷ ΔS (e.g. N₂ + 3H₂ → 2NH₃).
- QuestionHow is ΔG° related to K?Answer
ΔG° = −RT ln K (R = 8.314 J mol⁻¹ K⁻¹). Negative ΔG° means K greater than 1.
- QuestionDoes a negative ΔG mean a reaction is fast?Answer
No. It means the reaction can happen; its speed depends on the activation energy.
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