Question

What is observed at equilibrium point in the reaction?
${{PC}}{{{l}}_{{{5}}\left( {_{{g}}} \right)}}\, \rightleftharpoons \,\,{{PC}}{{{l}}_{{{3}}\left( {_{{g}}} \right)}}{{ + }}\,{{C}}{{{l}}_{{2}}}\,$
A. Equal volumes of ${{PC}}{{{l}}_{{{5}}\left( {_{{g}}} \right)}}$,${{PC}}{{{l}}_{{{3}}\left( {_{{g}}} \right)}}$ and ${{C}}{{{l}}_{{2}}}$ are present.
B. Equal masses of ${{PC}}{{{l}}_{{{5}}\left( {_{{g}}} \right)}}$,${{PC}}{{{l}}_{{{3}}\left( {_{{g}}} \right)}}$ and ${{C}}{{{l}}_{{2}}}$ are present.
C. The concentration of ${{PC}}{{{l}}_{{{5}}\left( {_{{g}}} \right)}}$,${{PC}}{{{l}}_{{{3}}\left( {_{{g}}} \right)}}$ and ${{C}}{{{l}}_{{2}}}$ become constant
D. Reaction comes to a stop.

Answer 1

During equilibrium, the rate of forward and backward reaction become equal, this is the state when the concentration of reactants equals the concentration of products. The rate of a reaction is the speed at which reaction takes place. The forward arrow shows the formation of product from reactant and the backward arrow shows the formation of reactants from product.

Complete step by step answer:
Equilibrium is the state of a system in which the concentration of the reactant and the concentration of the products do not change with time. It is a condition in which the rate of both forward and backward reaction are equal and there is no net change in the compositions.
chemical equilibrium can be categorised into two
A. Homogeneous Equilibrium
Here all the reactants and products are in the same phase.
${{{N}}_{{2}}}{{ }}\left( {{g}} \right){{ + }}{{{O}}_{{2}}}{{ }}\left( {{g}} \right) \rightleftharpoons {{2NO }}\left( {{g}} \right)$
Here both the reactant and product is in a gaseous state.
B. Heterogeneous Equilibrium
Equilibrium system having more than one phase is called heterogeneous Equilibrium ${{CaC}}{{{O}}_{{3}}}{{ }}\left( {{s}} \right) \rightleftharpoons {{CaO }}\left( {{s}} \right){{ + C}}{{{O}}_{{2}}}{{ }}\left( {{g}} \right)$
Here more than one phase is present.
Consider the reaction,
${{aA}}\,{{ + }}\,{{bB}} \rightleftarrows \,{{cC}}\,{{ + dD}}$
The equilibrium constant ${{{K}}_{{c}}}$ is the product of the concentrations of products raised to their stoichiometric coefficient divided by product of the concentrations of reactants raised to their stoichiometric coefficient.
${{{K}}_{{c}}}$ ${{ = }}\,\dfrac{{{{\left[ {{C}} \right]}^{{c}}}{{\left[ {{D}} \right]}^{{d}}}}}{{{{\left[ {{A}} \right]}^{{a}}}{{\left[ {{B}} \right]}^{{b}}}}}$
The factors affecting equilibria can be explained by Le Chatelier’s principle. It states that a change in any factor that determines the equilibrium conditions of a system will cause the system to change in such a manner to reduce the effect of change.
The factors that can influence the equilibrium are concentration, pressure, and temperature.
the correct answer is C, the concentration of ${{PC}}{{{l}}_{{{5}}\left( {_{{g}}} \right)}}$,${{PC}}{{{l}}_{{{3}}\left( {_{{g}}} \right)}}$ and ${{C}}{{{l}}_{{2}}}$ become constant.

So, the correct answer is C.

Additional information:
Equilibrium constant ${{{K}}_{{c}}}$ for a reverse reaction is the inverse of the equilibrium constant for the reaction in forward direction. Catalyst does not affect equilibrium but increases the rate of the chemical reaction.

Note: The equilibrium constant for exothermic reaction is negative and positive for endothermic reaction. In the endothermic reaction, products are less stable than the reactants while products are more stable than the reactants in exothermic reactions.