Chemical Thermodynamics Chapter 4 Chemistry Class 12 Textbook Solution

1) The total entropy change that accompanies a process is given by:

2) According to the second law of thermodynamics, for a process to be spontaneous, \( \Delta S_{\text{total}} > 0 \).

3) If \( \Delta H \) is the enthalpy change accompanying a reaction (system), the enthalpy change of the surroundings is \( -\Delta H \). Thus,

4) Substituting equation (2) into equation (1), we get:

Rearranging the above expression, we get:

5) The change in Gibbs energy at constant temperature and constant pressure is given by:

\[ \Delta G = \Delta H - T\Delta S \quad \text{(4)} \]

6) Substituting equation (3) into equation (4), we get:

\[ \Delta G = -T\Delta S_{\text{total}} \]

7) For a spontaneous reaction, \( \Delta S_{\text{total}} > 0 \), and hence, \( \Delta G < 0 \). At constant temperature and pressure, Gibbs energy of the system decreases in a spontaneous process.

8) The second law leads to the conditions of spontaneity as follows:

i) \( \Delta S_{\text{total}} > 0 \) and \( \Delta G < 0 \), the process is spontaneous.

ii) \( \Delta S_{\text{total}} < 0 \) and \( \Delta G > 0 \), the process is non-spontaneous.

iii) \( \Delta S_{\text{total}} = 0 \) and \( \Delta G = 0 \), the process is at equilibrium.