Question

Examine the given reaction.

Answer 1

Answer:

The correct option is;

D)

Explanation:

The given reaction is presented as follows;

NH₄Cl (s) → NH₃ (g) + HCl (g) ΔH° = 176 kJ/mol, ΔS° = 0.285 kJ/(mol·K)

We note that the Gibbs free energy, ΔG° is represented by the following equation;

ΔG° = ΔH° - T·ΔS°

Where:

T = Temperature (Kelvin)

The reaction will be spontaneous for exergonic reactions, ΔG° < 0 and it will not be spontaneous for endergonic reaction, ΔG° > 0

At room temperature, T = 25 + 273.15 = 298.15 K

Which gives;

ΔG° = 176  - 298.15 × 0.285 = 91.03 kJ/mol which is > 0 Not spontaneous reaction

At 800°C, we have;

T = 273.15 + 800°C  + 1073.15 K

ΔG° = 176  - 1073.15 * 0.285 = -129.85 kJ/mol which is < 0 the reaction will be spontaneous

The correct option is therefore, that at room temperature, the reaction is not spontaneous. However, at high temperatures. like 800 °C, the free energy value turns negative and this reaction becomes spontaneous.