Question

When two reactants, A and B are mixed to give products C and D such that
A + B $\leftrightharpoons$ C + D

the reaction quotient, Q = $\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$ at the final stages of the reaction

• A. is zero
• B. decreases with time
• C. is independent of time
• D. increases with time

Answer 1

The correct option is C

is independent of time

At equilibrium, the reaction quotient Q = $\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$ becomes a special constant called the equilibrium constant $K_c$ =$\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$. Once this system reaches equilibrium, all the macroscopic thermodynamic properties like Pressure(total), partial pressures or individual concentrations of each component, density of each component, internal energy, entropy, Free energy, Volume etc become constant.

The concentrations of C D A and B no longer change after equilibrium. Hence $K_c$ is constant for a particular given temperature at which the equilibrium is achieved. The reaction quotient becomes equal to $K_c$