Question

What is the equilibrium constant $K_{eq}$ for this reaction$:$ $aA+bB\rightleftharpoons cC+dD$, if A and D are solids?

• A. $\frac{\left[C{]}^c\right[D{]}^d}{\left[A{]}^a\right[B{]}^b}$
• B. $\frac{\left[A{]}^a\right[B{]}^b}{\left[C{]}^c\right[D{]}^d}$
• C. $\frac{[C{]}^c}{[B{]}^b}$
• D. $\frac{\left[C{]}^c\right[D{]}^d}{[A{]}^a}$
• E. $\left[A{]}^a\right[B{]}^b\left[C{]}^c\right[D{]}^d$

Answer 1

Answer: (C)

$\frac{[C{]}^c}{[B{]}^b}$

The equilibrium constant for the reaction $aA+bB\rightleftharpoons cC+dD$ is
$K=\frac{\left[C{]}^c\right[D{]}^d}{\left[A{]}^a\right[B{]}^b}$.
However, A and D are solids. Hence, their concentrations will not appear in the equilibrium constant expression. Hence, the equilibrium constant is
$K=\frac{[C{]}^c}{[B{]}^b}$.