Question

At $473$K, equilibrium constant, $K_c$ for decomposition of phosphorus pentachloride, $PC{l}_5$ is $8.3\times {10}^{-3}$. If decomposition is depicted as:
$PC{l}_{5\left(g\right)}\rightleftharpoons PC{l}_{3\left(g\right)}+C{l}_{2\left(g\right)};{△}_r{H}^0=124.0kmo{l}^{-1}$ what would be the effect on reaction if the temperature is increased?

• A. Reaction will shift in the backward direction.
• B. Reaction will shift in the forward direction.
• C. Reaction is equilibrium
• D. Reaction first moves forward and then remains at equilibrium.

Answer 1

The correct option is B Reaction will shift in the forward direction.

The given reaction is :-

${PCl}_5\left(g\right)\rightleftharpoons {PCl}_3\left(g\right)+{Cl}_2\left(g\right);{△H}^0=124{Kmol}^{-1}$

This reaction is endothermic reaction. So, if the temperature is increased then by applying Lechaterlier's principle, it can seen that forward reaction gets favoured.

So, more of ${PCl}_5$ will get dissociated to form ${PCl}_3\&{Cl}_2$.