For the reaction 2 + 2, the units of Kc are — Chemical Equilibrium Chemistry Question

💡 Solution & Explanation

# Finding Units of Kc for 2SO₂ + O₂ ⇌ 2SO₃ **Step 1: Write the expression for Kc** $$K_c = \frac{[SO_3]^2}{[SO_2]^2[O_2]}$$ **Step 2: Identify concentration units** Each concentration term has units of mol/L (or M, molarity). **Step 3: Substitute units into the expression** $$[K_c] = \frac{(\text{mol/L})^2}{(\text{mol/L})^2 \times (\text{mol/L})} = \frac{(\text{mol/L})^2}{(\text{mol/L})^3}$$ **Step 4: Simplify** $$[K_c] = (\text{mol/L})^{2-3} = (\text{mol/L})^{-1} = \frac{\text{L}}{\text{mol}}$$ Or equivalently: $\text{mol}^{-1}\text{L}$ or $\text{M}^{-1}$ **General Rule:** For any reaction, $[K_c] = (\text{mol/L})^{\Delta n}$ where $\Delta n = \text{(sum of product coefficients)} - \text{(sum of reactant coefficients)}$ Here: $\Delta n = 2 - (2+1) = -1$, so units are $(\text{mol/L})^{-1}$ ✓