Question

Concentration of a gas is expressed in the following terms in the calculation of equilibrium constant
A. No. of molecules per litre
B. No. of grams per litre
C. No. of gram equivalent per litre
D. No. of molecules equivalent per

Answer 1

Hint: To solve this question we have to know about units of concentration. In an equilibrium reaction the rate constant of the reaction is given as the ratio of concentration of product to the concentration of reactant. Any coefficient of the reactant or product is used as the power of the concentration. The unit of concentration is given as $mol.lite{{r}^{-1}}$.

Complete Step by Step Answer:
Equilibrium constant is a ratio of concentration of product to the concentration of reactant. Any coefficient of the reactant or product is used as the power of the concentration. We know that concentration is a ratio of mass and volume.
To calculate the equilibrium constant the mass of product and reactant is represented in terms of number of moles or the number of molecules of that product or reactant. The volume is represented in terms of litre. Thus the overall concentration is expressed as $mol.lite{{r}^{-1}}$ or in terms of number of molecules per litre.
Thus the concentration of a gas is expressed by the number of molecules per litre to calculate equilibrium constant.
Thus the correct option is A.

Note: An equilibrium reaction is that reaction where there is an equilibrium between the reactants and products of the reaction. Here the reaction can proceed in both the forward and backward directions that means reactants react to give product and again product can also break down into the corresponding reactants.