Practice question · Sort into groups
Sort each combination of signs by when the reaction is spontaneous.
Groups: At all temperatures · At no temperature · Only at high temperature · Only at low temperature
- +ΔH and -ΔS
- -ΔH and -ΔS
- +ΔH and +ΔS
- -ΔH and +ΔS
Hints
- Both terms favourable means always; both unfavourable means never.
- When they disagree, the temperature decides which one wins.
Show the answer
At all temperatures: -ΔH and +ΔS
At no temperature: +ΔH and -ΔS
Only at high temperature: +ΔH and +ΔS
Only at low temperature: -ΔH and -ΔS
Why
When enthalpy and entropy agree, temperature is irrelevant. When they disagree, the term grows with temperature, so a positive needs high to win and a negative one needs low to stay out of the way.
Practise Gibbs Free Energy and Spontaneity
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