Question

Which one of the following has ${\Delta S}^o$ positive?

• A. $CaO\left(s\right)+{CO}_2\left(g\right)\rightleftharpoons {CaCO}_3\left(s\right)$
• B. $NaCl\left(aq\right)\rightleftharpoons NaCl\left(s\right)$
• C. ${NaNO}_3\left(s\right)+H_{2}O\rightleftharpoons {Na}^{+}\left(aq\right)+{NO}_3^{-}\left(aq\right)$
• D. $N_2\left(g\right)+{3H}_2\left(g\right)\rightleftharpoons {2NH}_3\left(g\right)$

Answer 1

The correct option is C ${NaNO}_3\left(s\right)+H_{2}O\rightleftharpoons {Na}^{+}\left(aq\right)+{NO}_3^{-}\left(aq\right)$

Dissolution of compound in solvent increases entropy.

In other option, no. of gas molecules in reactant is greater than no. of molecule in product. Hence there will be more randomness in the reactant than product.

So, $△S^o$ is -ve
$△S^o$ is +ve only in option c.