Question

When a large amount of sodium hydroxide is added to water at 25 ⁰C, some of it dissolves and the temperature of the system increases. Predict how the enthalpy, entropy, and free energy change in the system during this process. Explain the basis for each of your predictions.

Answer 1

Solution:

When NaOH is dissolved in water, then the following reaction take place,
NaOH(s) + H2O(l) = Na+(aq) + OH-(aq) + Heat

Therefore,
> The entropy increases because disorder increases during solvation process.

Thus, ΔS = + ve
> The bonds are being broken during the solvation process which leads to increase the temperature of the system and therefore reaction is exothermic.

Thus, ΔH = - ve

> Free energy change ( ΔG) is calculated as,

ΔG = ΔH - T ΔS

ΔG = - ΔH - T ΔS = - ve

Thus,

ΔG = - ve

Hence, reaction is feasible.