Q. The effect of temperature on spontaneity of reactions are represented as : [table] | ΔH | ΔS | Temperature | Spontaneity ; (A) | + | − | any T | Non spontaneous ; (B) | + | + | low T | spontaneous ; (C) | − | − | low T | Non spontaneous ; (D) | − | + | any T | spontaneous [/table]
A) (B) and (C) only
B) (B) and (D) only
C) (A) and (D) only
D) (A) and (C) only
Explanation
[Solution by Dr. Abubacker] From $\Delta G=\Delta H-T\Delta S$: (A) $\Delta H>0,\Delta S<0$ is non-spontaneous at any $T$ (correctly represented). (D) $\Delta H<0,\Delta S>0$ is spontaneous at any $T$ (correct). (B) $\Delta H>0,\Delta S>0$ is spontaneous only at high $T$, so 'low T, spontaneous' is wrong. (C) $\Delta H<0,\Delta S<0$ is spontaneous at low $T$, so 'low T, non spontaneous' is wrong. The key option (B) and (C) corresponds to the two wrongly represented entries. (Medium confidence: the stem as printed does not say 'incorrect'; this follows the official key.) Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.