For the given reaction: 2A(s) + B(g) ⇌ C(g) + 2D(s) + E(s), the extent of B was found to be 20% at 3 — Chemical Equilibrium Chemistry Question

💡 Solution & Explanation

Step 1 - Express the Rate of the Backward Reaction For the given heterogeneous equilibrium: \[\ce{2A(s) + B(g) <=> C(g) + 2D(s) + E(s)}\] The backward reaction is: \[\ce{C(g) + 2D(s) + E(s) -> 2A(s) + B(g)}\] The rate of the backward reaction depends only on the gaseous component \ce{C(g)} and the backward rate constant \(k_b\): \[r_b = k_b [\ce{C}]\] Step 2 - Analyze the Dependence of the Rate Constant on Temperature (Arrhenius Equation) According to the Arrhenius equation: \[k = A e^{-\frac{E_a}{RT}}\] As temperature increases, the exponential term \(e^{-E_a/RT}\) increases, so the backward rate constant \(k_b\) always increases with temperature, regardless of whether the reaction is exothermic or endothermic. Step 3 - Analyze the Dependence on Pressure The rate constant of a chemical reaction is entirely independent of pressure. An increase or decrease in external pressure does not change the value of \(k_b\). While pressure can shift the equilibrium position (Le Chatelier), it does not alter rate constants. Step 4 - Evaluate the Options * **Option (A)**: Incorrect. The rate constant is independent of pressure. * **Option (B)**: Incorrect. The rate increases (not decreases) with temperature, and is independent of pressure. * **Option (C)**: Incorrect. The backward rate increases with temperature, not decreases. * **Option (D)**: Correct. The rate of backward reaction depends only on temperature and increases with temperature. \[\boxed{\text{D}}\]