`PCl_(5)` can be formed by heating a mixture of `Cl_(2) " and " PCl_(3)`. If 1 mole each of `Cl_(2) " and " PCl_(3)` are mixed and the reaction is allowed to take place in a closed container fitted with a pressure gauge and explain with a suitable reason.

Explanation

`PCl_(3(g))+Cl_(2(g)) hArr PCl_(5(g))`. The number of moles of products is half the number of moles of the reactants. If the reaction goes to completion, we should expect that the pressure indicator should show half of the initial pressure. But the pressure indicator indicates a higher pressure than half of the initial pressure and it is less than the initial pressure. This indicates that the reaction did not go to completion. Later if the pressure indicator shows constant value without further rise or fall in pressure, it implies that the reaction is in equilibrium. The pressure gauge inititally shows decrease followed by an increase ultimately reaching a constant position which indicates the equilibrium.