question_answer 1)

For the reaction at 298 K : \[2A+B\to C\] \[\Delta H=400kJ\,mo{{l}^{-1}},\Delta S=2kJ\,\,{{K}^{-1}}mo{{l}^{-1}}\] At what temperature will the reaction become spontaneous considering \[\Delta H\] and \[\Delta S\] to be constant over the temperature range?  

Answer:

Information shadow: \[\Delta H=400\times {{10}^{3}}J\,mo{{l}^{-1}}\] \[\Delta S=2000J{{K}^{-1}}mo{{l}^{-1}}\] Problem solving strategy: A reaction is spontaneous, when \[\Delta G=-ve\] \[\therefore \] \[(\Delta H-T\Delta S)\frac{\Delta H}{\Delta S}\] Working it out: \[T>\frac{400\times 1000}{2000}\] \[T>200K\] Reaction will be spontaneous above 200 K.