Question

`Delta Hc^(-)` (the standard enthalpy of combustion) of butane and 2-methyl propane is `-2877.0` and `-2868.0` kJ `mol^(-1)`, respectively. Explain the relative stabilities of the two isomers.

Answer 1

On combustion, the same number of C atoms gives the same number of moels of `CO_(2)` and `H_(2)O`. So a direct comparison is not possible. Greater the negative value of combustion, thermodyna-mically less stable is the combustion than isobutane (2-methyl propane), it must contain relatively more potential energy. Isobutane, therefore, is more stable than butane by 9 kJ `mol^(-1)` as shown in the graph below.