Question

For a gas phase reaction, what do you concentrate on topredict the sign of $\mathbf{∆}\mathbf{S}$? For a phase change, what do you concentrate on to predict the sign of $\mathbf{∆}\mathbf{S}$? That is, how are ${\mathbf{S}}_{\mathbf{solid}\mathbf{,}}^{\mathbf{°}}{\mathbf{S}}_{\mathbf{liquid}\mathbf{,}}^{\mathbf{°}}\mathbf{and}\mathbf{}{\mathbf{S}}_{\mathbf{gas}}^{\mathbf{°}}$related to one another? When a solute dissolves in water, what is usually the sign of$\mathbf{∆}\mathbf{S}$ for this process?

Short answer

Answer

The order of entropy for gas phase, liquid phase and the gas phaseis $\mathbf{∆}{\mathbf{S}}_{\mathbf{solid}}^{\mathbf{°}}\mathbf{<}\mathbf{∆}{\mathbf{S}}_{\mathbf{liquid}}^{\mathbf{°}}\mathbf{<}\mathbf{∆}{\mathbf{S}}_{\mathbf{gas}}^{\mathbf{°}}$.

Thesign of $\mathbf{∆}\mathbf{S}$for this process is entropywhich is increasing.

Step-by-step solution

Step 1: Introduction to the Concept

The ratio of thermal energy to the temperature at which work cannot be done is known as entropy.It's also known as the measure of a system's molecular disarray. It has a lot of properties and state functions.

The number of microstates for a system is connected to entropy, and microstate is defined as the number of possible arrangements for the system.

Step 2: Solution Explanation

The amount of moles of gases present in the reactants and products sides predicts the sign of entropy change in a gas phase reaction.

When there are more moles of gas in the reactants than in the products, the entropy change is negative, but when there are fewer moles of gas in the reactants than in the products, the entropy change is positive. It's difficult to anticipate the sign of entropy change when the amount of moles of gas on both sides (reactant and product) is equal.

Entropy variesdepending on thephase of the material in various physical states.

The entropy change is reducedin the solid state due to the presence of little randomness.

Because the liquid stateis slightly disorderedcompared to the solid state, the entropy change is greater than the solid state.

Because the gaseous state is more disordered than the liquid state, the entropy change isgreater.

Thus the order of the entropy is as follows,

$\mathbf{∆}{\mathbf{S}}_{\mathbf{solid}}^{\mathbf{°}}\mathbf{<}\mathbf{∆}{\mathbf{S}}_{\mathbf{liquid}}^{\mathbf{°}}\mathbf{<}\mathbf{∆}{\mathbf{S}}_{\mathbf{gas}}^{\mathbf{°}}$

When a solute is combined with a solvent,the process becomes more disordered, or the unpredictability increases.

As a result, entropy rises and i.e.$\mathbf{∆}{\mathbf{S}}^{\mathbf{°}}\mathbf{>}\mathbf{0}.$