Question

For which of the following reactions is $\mathbf{∆}\mathbf{S}\mathbf{°}$a positive value?

a.

b.

Short answer

Answer

1. $∆\mathrm{S}°$is positive.
2. No change in $∆\mathrm{S}°$.

Step-by-step solution

Step-by-Step SolutionStep 1: Entropy Change

The entropy change is the change in the randomness of the system when the reactants undergo a reaction to form products.

Conventionally, the value of entropy $∆\mathrm{S}°$should be higher for products.

Comparison of Entropy for reactants and products

When two reactants combine to form a single product, the disorderliness decreases. Hence, the entropy of the system decreases in going from reactants to products.

When a single reactant dissociates to form two or more products, the randomness in the products increases, hence, the entropy of the products increases, and that is favored.

Explanation

1. Since the number of molecules in the products is more than the number of molecules of reactants the entropy of the products is more. Hence, $∆\mathrm{S}°$is positive.
2. The number of molecules of reactants and products is the same. Hence, there is no change in the entropy of the system. So, neither of the products or the reactants are favored.