Thermodynamics — Medium JEE chemistry MCQ
For a reaction to be spontaneous at all temperatures, which of the following conditions must be satisfied?
- A. ΔH > 0, ΔS > 0
- B. ΔH < 0, ΔS < 0
- C. ΔH < 0, ΔS > 0
- D. ΔH > 0, ΔS < 0
Solution
For spontaneity, Gibbs free energy change must be negative:
\[
\Delta G = \Delta H - T\Delta S < 0
\]
For a reaction to be spontaneous at all temperatures:
- If ΔH < 0 (exothermic) and ΔS > 0 (entropy increases), then:
- ΔG = (negative) - T(positive) = negative for all T > 0
This is the only combination that guarantees ΔG < 0 at all temperatures.
So the correct option is C.