JEE Advanced levelSingle correct optionDifficulty 3 of 3g3207
Reactant A gives P1 and P2 by parallel first-order steps with k1=4.0×10−2s−1 and k2=1.0×10−2s−1. Each product can also revert to A, and at equilibrium [P2]/[P1]=9.0. The product distribution early in the reaction and at equilibrium respectively is
A80% P2 initially; 90% P1 at equilibrium
B80% P1 initially; 90% P2 at equilibrium
C50% each initially; 90% P2 at equilibrium
D80% P1 initially; 90% P1 at equilibrium
Answer: B
Early on, reversal is negligible, so [P1]/[P2]=k1/k2=4.0, i.e. 80% P1 (kinetic). At equilibrium the ratio is set by K: P2 fraction =9/(1+9)=90% (thermodynamic).