Question

x moles and y moles per litre of A and B respectively were allowed to react. At the equilibrium $A(g)+2B(g)\to \dfrac{1}{2}C(g)$. The concentration of A, B and C were found to be 4, 2 and 2 moles/litre respectively. Value of x and y is:
A. 6 and 4
B. 8 and 10
C. 6 and 10
D. 8 and 4

Answer 1

Hint: Chemical equilibrium refers to the state wherein both the reactants and the products present in the concentration have no tendency to change with the period of time during a chemical reaction.

Complete step by step answer:
A chemical reaction achieves chemical equilibrium when the rate of forward reaction and that of the reverse reaction is the same.
Since, the rates are equal and there is no net change in the concentrations of the reactants and the products – the state is referred to as a dynamic equilibrium and the rate constant is known as equilibrium constant.
The equilibrium constant is defined as the product of the molar concentration of the products which is each raised to the power equal to its stoichiometric coefficients divided by the product of the molar concentrations of the reactants, each raised to the power equal to its stoichiometric coefficients is constant at constant temperature.

For the reaction $A(g)+2B(g)\to \dfrac{1}{2}C(g)$.
So, 0.5 moles of C requires = 1 mole of A
2 moles of C require = $\dfrac{1}{0.5}\times 2$ = 4 moles of A
Similarly, 0.5 moles of C requires = 2 mole of B
2 moles of C require = $\dfrac{2}{0.5}\times 2$= 8 moles of B.
Hence, the value of x and y is 4 and 8.
So, the correct answer is “Option D”.

Note: ways remember, a chemical reaction achieves chemical equilibrium when the rate of forward reaction and that of the reverse reaction is the same.
Factors affecting the equilibrium are concentration, temperature and pressure.
Addition of catalyst and inert gas do not have any effect on equilibrium.