how is the concept of coupling reactions useful in explaining the occurrence of non-spontaneous thermochemical reactions?

Asked by ganeshadode64 adode | 30th Oct, 2013, 12:34: PM

Expert Answer:

Coupling reactions:

Many reactions which are non-spontaneous (?G is +ve) can be made to occur spontaneously if these are coupled with reactions having larger negative free energy.

By coupling means both non-spontaneous and spontaneous reactions can be carried out simultaneously.

For example:

Decomposition of Fe2O3 into iron is a non-spontaneous reaction. However this decomposition can take place simultaneously if carbon monoxide is simultaneously burnt in oxygen.

                2Fe2O3 ? 4Fe + 3O2     ----- (1) ?G0 = +1487kJmol-1

             2CO + O2 ? 2CO2       -----      (2) ?G0 = - 514kJmol-1

Multiplying equation (2) by 3 and then adding to equation (1) we get

             6CO + 3O2 ? 6CO2        ?G0 = - 1543kJmol-1

                2Fe2O3     ? 4Fe + 3O2  ?G0 = +1487kJmol-1

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    2Fe2O3   + 6CO ? 4Fe   + 6CO2    ?G0 = -56.2Kjmol-1

Answered by Vaibhav Chavan | 30th Oct, 2013, 05:57: PM

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