A mixture of two substances A and B gives the same product C by two parallel first-order reactions: A → C and B → C. If the initial concentrations of A and B are 1.0 and 0.8 M, respectively, and their

Question

A mixture of two substances A and B gives the same product C by two parallel first-order reactions: A → C and B → C. If the initial concentrations of A and B are 1.0 and 0.8 M, respectively, and their half-lives, Ta and Tb, are 10 min and 15 min, respectively, the concentration of C (in millimole per litre) after 30 min?

Prashant Kotian · Accepted Answer

Correct answer: 1475. For A (10 min half-life), 30 min is 3 half-lives. A remaining = 1.0 / 8 = 0.125 M, so A reacted = 0.875 M. For B (15 min half-life), 30 min is 2 half-lives. B remaining = 0.8 / 4 = 0.2 M, so B reacted = 0.6 M. C produced = A reacted + B reacted = 0.875 + 0.6 = 1.475 M. Converting to millimoles per litre gives 1475. Therefore, correct answer is 1475.

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