Consider the heterogeneous equilibrium . Initially, of solid and of gas are placed in a flask. If at — Chemical Equilibrium Chemistry Question
Question
Consider the heterogeneous equilibrium $A(s) + B(g) \rightleftharpoons C(g)$. Initially, $5.0\text{ moles}$ of solid $A$ and $2.0\text{ moles}$ of gas $B$ are placed in a $10\text{ L}$ flask. If at equilibrium, the active mass of $B$ is found to be $0.15\text{ M}$, calculate the number of moles of solid $A$ remaining in the flask.
💡 Solution & Explanation
Initial concentration of $B = \frac{2.0}{10} = 0.20\text{ M}$. Equilibrium concentration of $B = 0.15\text{ M}$. Change in concentration of $B = 0.20 - 0.15 = 0.05\text{ M}$. Moles of $B$ reacted $= 0.05\text{ M} \times 10\text{ L} = 0.5\text{ moles}$. From stoichiometry, $1\text{ mole}$ of $A$ reacts per mole of $B$. So, $0.5\text{ moles}$ of $A$ reacted. Remaining moles of $A = 5.0 - 0.5 = 4.5\text{ moles}$.