Question

For which of the following is there an increase in entropy?

• A. $Na\left(s\right)+H_{2}O\left(l\right)\to NaOH\left(aq\right)+H_2\left(g\right)$
• B. $I_2\left(g\right)\to I_2\left(s\right)$
• C. $H_{2}S{O}_4\left(aq\right)+Ba\left(OH{)}_2\right(aq)\to BaS{O}_4(s)+H_{2}O(l)$
• D. $H_2\left(g\right)+1/2O_2\left(g\right)\to H_{2}O\left(l\right)$
• E. None of the above

Answer 1

Answer: (A)

$Na\left(s\right)+H_{2}O\left(l\right)\to NaOH\left(aq\right)+H_2\left(g\right)$

Option A is the correct answer. Entropy will be increased in this case.

$Na$ $+$ $H_{2}O$ $\to$ $NaOH\left(aq\right)$ $+$ $H_2\left(g\right)$

Entropy means randomness. The products formed in this case are aqueous and gaseous in nature. Aqueous and gaseous solutions will have more randomness than solid, because in aqueous and gaseous solutions the molecules are far apart from each other than in solid. Hence entropy or randomness will be more for aqueous and gaseous solutions.

In all the other cases randomness will be less in the product as we see in one case solid is formed and in another case the number of moles in the product is less than the number of moles in reactant.