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

`DeltaG^@=DeltaG^@`+RT ln Q
`DeltaG` =Change in free energy of the reaction
`DeltaG^@` =Standard free energy change
Q=Reaction quotient
R=Gas constant , T=temperature (K)
(a) Since `DeltaG^@`=-RT ln K
`DeltaG=-RT ln K + RT ln Q=RT ln Q/K`
If Q < K , `DeltaG` =-ve . Therefore , reaction proceeds in the forward direction.
If Q=K , `DeltaG=0` , Reaction is at equilibrium and no net reaction occurs.
(b)`K_c=([CH_4][H_2O])/([CO][H_2]^(3))`
If pressure is increased , then volume will decrease. Let pressure is doubled so that volume is reduced to half. The molar concentration will become double.
`Q_c=(2[CH_4]2[H_2O])/(2[CO][2H_2]^3)`
`=1/4 ([CH_4][H_2O])/([CO][H_2]^3)=1/4K_c`
Thus , `Q_c` is less than `K_c`. Therefore , to re-establish the equilibrium , `Q_c` will tend to increase and equilibrium will shift in the forward direction.