Question

What is observed at equilibrium point in the reaction?
$PC{l}_{5\left(g\right)}\rightleftharpoons PC{l}_{3\left(g\right)}+C{l}_{2\left(g\right)}$

• A. Equal volumes of $PC{l}_5,PC{l}_{3}andC{l}_2$ are present
• B. Equal masses of $PC{l}_5,PC{l}_{3}andC{l}_2$ are present
• C. The concentration of $PC{l}_5,PC{l}_{3}andC{l}_2$ become constant
• D. Reaction comes to a stop

Answer 1

Answer: (C)

The concentration of $PC{l}_5,PC{l}_{3}andC{l}_2$ become constant

The definition of chemical equilibrium is the point at which the concentrations of reactants and products do not change with time. It appears as though the reaction has stopped but in fact, the rates of the forward and reverse reactions are equal so reactants and products are being created at the same rate and are constant.

The equilibrium constant of the reaction can be determined by:

$K_c=\frac{\left[PC{l}_5\right]}{\left[PC{l}_3\right]+\left[C{l}_2\right]}$

$K_c$ is the equilibrium const, if $K_c>>1$ then forward reaction is favoured i.e more products are formed, and if $K_c<<1$, then backward reaction is favoured i.e more reactants are formed, and if $K_c=1$, then the reaction is at equilibrium and the concentration of the reactants and products are equal.