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For the reaction A -> n B, the concentration of A decreases with time while concentration of B increases. At the point where the concentration–time curves of A and B intersect each other, the concentration of B at that instant is expressed in terms of the initial concentration A0 and stoichiometric coefficient n. Which of the following correctly gives [B] at the intersection point?

1. n * A0 / 2
2. A0 / (2n - 1)
3. n * A0 / (n + 1)
4. 2n * A0 / (n + 1)

Correct answer: n * A0 / (n + 1)

Solution

At the intersection, [A] = [B]. From stoichiometry, if A0 - x = [A] and [B] = n*x, setting them equal gives A0 - x = n*x, so x = A0/(n+1) and [B] = n*A0/(n+1).

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