NEET 2017 · ChemistryPrevious Year Question

For a given reaction, $Δ H = 35.5 k J m o l^{- 1}$ and $Δ S = 83.6 J K^{- 1} m o l^{- 1}$ . The reaction is spontaneous at: (Assume that $Δ H$ and $Δ S$ do not vary with temperature.)

Answer: (B) $T > 425 K$ . \textbf{Answer:} (B) $T > 425 K$ \textbf{Solution:} The reaction is spontaneous when $Δ G = Δ H - T Δ S < 0$ .

A. $T < 425 K$
B. $T > 425 K$ ✓
C.All temperatures
D. $T > 298 K$

Correct Answer

(B) $T > 425 K$

Solution & Explanation

\textbf{Answer:} (B) $T > 425 K$ \textbf{Solution:} The reaction is spontaneous when $Δ G = Δ H - T Δ S < 0$ . Both $Δ H$ and $Δ S$ are positive, so spontaneity requires $T Δ S > Δ H$ , i.e. $T > \frac{Δ H}{Δ S} = \frac{35.5 \times 1 0 ^{3} J}{83.6 J K ^{- 1}} \approx 425 K$ . Hence the reaction is spontaneous at $T > 425 K$ .

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For a given reaction, ΔH=35.5 kJmol−1 and ΔS=83.6 JK−1mol−1. The reaction is spontaneous at: (Assume that ΔH and ΔS do not vary with temperature.)

Solution & Explanation

More NEET PYQ solutions

For a given reaction, $Δ H = 35.5 k J m o l^{- 1}$ and $Δ S = 83.6 J K^{- 1} m o l^{- 1}$ . The reaction is spontaneous at: (Assume that $Δ H$ and $Δ S$ do not vary with temperature.)