Write a relation between `DeltaG` and Q and deifine the meaning of each term and answer the following :
Why a reaction proceeds forward when `QltK` and no net reaction occure when `Q=K`.
Explain the effect of increase in presure in terms of reaction quotient Q for the reaction : `CO(g)+3H_2(g)hArrCH_4(g)+H_2O(g)`

Explanation

`Delta G = DeltaG^(@)` + RT ln Q
where `Delta G =` Change in free energy as the reaction proceeds
`Delta G^(@) = ` Standard free energy change
Q = Reaction quotient
R = Gas constant
and T= temperature in K
(a) As `Delta G^(@) = - ` RT ln K
`:. Delta G = - RT` ln K + RT ln Q = RT ln `(Q)/(K)`
If `Q lt K, Delta G` will be -ve. Reaction will proceed in the forward direction.
If `Q=K, DeltaG=0`. Reaction is in equilibrium and there is no net reaction .
(b) `K_(c)=([CH_(4)][H_(2)O])/([CO][H_(2)]^(3))`. If pressure is increased, volume decreases. Suppose presure is doubled, volume will be halved. Hence, molar concentrations will be doubled.
Now `Q_(c) = ({2[CH_(4)]}{2[H_(2)O]})/({2[CO]}{2[H_(2)]}^(3))=(1[CH_(4)][H_(2)O])/(4[CO][H_(2)]^(3))=(1)/(4) K_(c)`
This, `Q_(c)` is less than `K_(c)`. Hence, to re-establish equilibrium , `Q_(c) ` will tend to increase , i.e., equilibrium will shift in the forward direction.