For a given reaction, = 35.5kJmo l ^ - 1 and = 83.6J K ^ - 1 mo l ^ - 1 . The reaction is spontaneous at : (Assume that and do not vary with temperature)

Correct answer: B. T > 425 K ∵ = - T For a reaction to be spontaneous, = - ve i.e., ∴ T > = 35.5 × 10 ^ 3 J 83.6J K ^ - 1 i.e., T > 425K

NEET 2017

NEET 2017 · Chemistry · Thermodynamics (C)

For a given reaction, = 35.5kJmo l ^ - 1 and = 83.6J K ^ - 1 mo l ^...

For a given reaction,

\text{\Delta}\text{H} = 35.5\text{k}\text{J}\text{m}\text{o}{\text{l}}^{- 1}

and

\text{\Delta}\text{S} = 83.6\text{J}{\text{K}}^{- 1}\text{m}\text{o}{\text{l}}^{- 1} .

The reaction is spontaneous at : (Assume that

\text{\Delta}\text{H}

and

\text{\Delta}\text{S}

do not vary with temperature)

B. T > 425 K

∵ \text{\Delta}\text{G} = \text{\Delta}\text{H} - \text{T}\text{\Delta}\text{S}

For a reaction to be spontaneous,

\text{\Delta}\text{G} = - \text{v}\text{e}

i.e.,

\text{\Delta}\text{H} < \text{T}\text{\Delta}\text{S}

∴ \text{T} > \dfrac{\text{\Delta}\text{H}}{\text{\Delta}\text{S}} = \dfrac{35.5 \times {10}^{3}\text{J}}{83.6\text{J}{\text{K}}^{- 1}}

i.e.,

\text{T} > 425\text{K}