COLUMN-I COLUMN-II (Sign of Δ H and Δ S respectively)(Nature of reaction) (A) − & − (P) Spontaneous only at low temperature (B) − & + (Q) Spontaneous only at high temperature (C) + & + (R) Spontaneous

Question

COLUMN-I COLUMN-II (Sign of Δ H and Δ S respectively)(Nature of reaction) (A) − & − (P) Spontaneous only at low temperature (B) − & + (Q) Spontaneous only at high temperature (C) + & + (R) Spontaneous at all temperatures (D) + & − (S) Non-spontaneous at all temperatures

TestHub · Accepted Answer

The spontaneity of a reaction is determined by the Gibbs Free Energy equation:

$Δ G = Δ H - T Δ S$

where a reaction is spontaneous if $Δ G < 0$ .

(A) $Δ H$ (–), $Δ S$ (–): $Δ G$ is negative only when $T$ is small enough that $Δ H > T Δ S$ . Matches (P) spontaneous at low temperatures.

(B) $Δ H$ (–), $Δ S$ (+): Both terms are negative, making $Δ G$ always negative. Matches (R) spontaneous at all temperatures.

(C) $Δ H$ (+), $Δ S$ (+): $Δ G$ becomes negative only when $T$ is large enough that $T Δ S > Δ H$ . Matches (Q) spontaneous at high temperatures.

(D) $Δ H$ (+), $Δ S$ (–): Both terms are positive, so $Δ G$ is always positive. Matches (S) non-spontaneous at all temperatures.

Chemistry - Thermodynamics - II Question with Solution | TestHub

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