Question

For the reaction A + B $\leftrightharpoons$ C + D the equilibrium constant is

• A. K = $\frac{\left[A\right]\left[B\right]}{\left[C\right]\left[D\right]}$
• B. K = $\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$
• C. both a & b
• D. None of these

Answer 1

The correct option is B

K = $\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$

aA + bB $\leftrightharpoons$ cC + dD

The rate of forward reaction = $k_1$ ${\left[A\right]}^a$ ${\left[B\right]}^b$

The rate of backward reaction = $k_2$ ${\left[C\right]}^c$ ${\left[D\right]}^d$

At Equilibrium, the rate of the backward reaction = the rate of the forward reaction

$k_2$ ${\left[C\right]}^c$ ${\left[D\right]}^d$ = $k_1$ ${\left[A\right]}^a$ ${\left[B\right]}^b$

K = $\frac{k_1}{k_2}$ = $\frac{{\left[C\right]}^c[D{]}^d}{{\left[A\right]}^a[B{]}^b}$