Question

Does the number of moles of reaction products increase, decrease or remain same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?
(a) ${PCl}_5\left(g\right)\rightleftharpoons {PCl}_3\left(g\right){Cl}_2\left(g\right)$
(b) $CaO\left(s\right)+{CO}_2\left(g\right)\rightleftharpoons {CaCO}_3\left(s\right)$
(c) $3Fe\left(s\right)+4H_{2}O\left(g\right)\rightleftharpoons {Fe}_3{O}_4\left(s\right)+4H_2\left(g\right)$

Answer 1

(a) The change in the number of moles of the gaseous species $\Delta n=1+1-1=1>0$. Hence, the number moles of reaction product increase by decrease in pressure due to increase in volume.
(b) The change in the number of moles of the gaseous species $\Delta n=0-1=-1=<1$. Hence, the number moles of reaction product decrease by decrease in pressure due to increase in volume.
(c) The change in the number of moles of the gaseous species $\Delta n=4-4=0$. Hence, the number moles of reaction product remains same due to decrease in pressure due to increase in volume.