For the reaction `N_(2)(g) + 3H_(2) rarr 2NH_(3)(g)`
`Delta H = – 95.4 kJ and Delta S = -198.3 JK^(-1)`
Calculate the temperature at which Gibbs energy change `(Delta G)` is equal to zero. Predict the nature of the reaction at this temperature and above it.
`Delta H = – 95.4 kJ and Delta S = -198.3 JK^(-1)`
Calculate the temperature at which Gibbs energy change `(Delta G)` is equal to zero. Predict the nature of the reaction at this temperature and above it.
`Delta G = Delta H – T Delta S`
`Delta G = 0`
`Delta H – T Delta S = 0`
or `Delta H = T Delta S`
`T = (Delta H)/(Delta S)=(-95.4 xx 1000 J)/(-198.3 JK^(-1))=481 K`
At this temperature, the reaction would be in equilibrium and with the increase in temperature the opposing factor `T Delta S` would become more and hence, `Delta G` would become positive and the reaction would become non-spontaneous. The reaction would be spontaneous at the temperature below 481 K.