Question

For a reaction if $K_p > K_c$ the forward reaction is favoured by (T > 15 K)

• A. High temperature
• B. Low temperature
• C. Low pressure
• D. High pressure

Answer 1

Answer: (C)

Low pressure

Answer 2

$K_p = K_c (RT)^{\Delta ng}$
or $\frac{K_p}{K_c} = (RT)^{\Delta ng}$
Now, $K_p > K_c$ (given) $\Rightarrow \frac{K_p}{K_c} > 1$
$(RT)^{\Delta n_g} > 1$
At T > 15 K
RT > 0.0821 $\times$ 15 L atm mol$^{-1}$
RT > 1.22 L atm mol$^{-1}$
$\Rightarrow$ $\Delta n_g > 0$
$\Rightarrow$ No. of moles of gaseous products > No. of moles of gaseous reactants
Such a reaction in the forward direction will be favoured by low pressure.