Chemical Kinetics Trick — Relation Between Pt and P∞ Explained ⚡
❓ Question A(g) → B(g) + C(g) is a first-order reaction . The reaction is followed using pressure method . Let: P t P_t = total pressure at time t t t P ∞ P_\infty = total pressure at infinite time Reaction started with only A Which of the following expressions gives the correct rate constant k k ? 🖼️ Question Image ✍️ Short Solution To derive the expression for k k , use pressure as a measure of extent of reaction . 🔹 Step 1 — Initial condition Reaction: A → B + C A \rightarrow B + C Initial pressure of A: P A = P 0 P_A = P_0 🔹 Step 2 — Pressure at time t t Let x x x be the amount (in pressure units) of A decomposed at time t t . Then: Pressure of A remaining = P 0 − x P_0 - x Pressure of B formed = x x Pressure of C formed = x x Total pressure at time t t t : P t = ( P 0 − x ) + x + x = P 0 + x P_t = (P_0 - x) + x + x = P_0 + x So: x = P t − P 0 x = P_t - P_0 🔹 Step 3 — Total pressure at infinite time When rea...