For the reaction , of and of are initially placed in a flask. At a certain time , the concentration — Chemical Equilibrium Chemistry Question
Question
For the reaction $A(g) + B(g) \rightleftharpoons C(g) + D(g)$, $1\text{ mole}$ of $A$ and $1\text{ mole}$ of $B$ are initially placed in a $1\text{ L}$ flask. At a certain time $t$, the concentration of $C$ is found to be $0.4\text{ M}$ and the concentration of $D$ is $0.4\text{ M}$. What is the value of the reaction quotient $Q_c$ multiplied by $9$?
💡 Solution & Explanation
From stoichiometry, since $0.4\text{ M}$ of $C$ and $D$ formed, $0.4\text{ M}$ of $A$ and $B$ must have reacted. The instantaneous concentrations are: $[A] = 1 - 0.4 = 0.6\text{ M}$, $[B] = 1 - 0.4 = 0.6\text{ M}$, $[C] = 0.4\text{ M}$, $[D] = 0.4\text{ M}$. $Q_c = \frac{[C][D]}{[A][B]} = \frac{0.4 \times 0.4}{0.6 \times 0.6} = \frac{0.16}{0.36} = \frac{16}{36} = \frac{4}{9}$. Therefore, $9 \times Q_c = 9 \times (4/9) = 4$.