question_answer

Comment on the validity of the following statements, giving reasons: (i) Thermodynamically, an exothermic reaction is sometimes not spontaneous. (ii) The entropy of steam is more than that of water at its boiling point (iii) The equilibrium constant for a reaction is one or more if \[{{\Delta }_{r}}G{}^\circ \] for it is less than zero.

Answer:

                (i) Yes, the given statement is true. This is because \[\Delta G=\Delta H-T\Delta S\]. For exothermic reaction, \[\Delta H\] is -ve. If \[T\Delta S\] is +ve (i.e., entropy factor opposes the process) and\[T\Delta S>\Delta H\]  in magnitude, \[\Delta G\] will be +ve and process will not be spontaneous. (ii) Yes, the given statement is true. This is because at the same temperature, gaseous state is more disordered than the liquid state. (iii)\[-\Delta {{G}^{o}}\,=RT\,\ln \,K\]. Thus, if \[\Delta {{G}^{o}}\] is less than zero, i.e., it is -ve, then \[\,\ln \,K\]will be +ve and hence K will be greater than 1.