Consider the second-order reaction aA → products (which has a first half-life of 25 s). If the concentration of A after 15.6s is 0.36M, determine the initial concentration of A.

Question

Quizplus · Accepted Answer

For a second-order reaction, the relationship between concentration and time is given by $\frac{1}{[A]} = \frac{1}{[A]_0} + kt$, where $[A]$ is the concentration at time $t$, $[A]_0$ is the initial concentration, and $k$ is the rate constant. The half-life ($t_{1/2}$) for a second-order reaction is given by $\frac{1}{k[A]_0}$. Given the first half-life is 25s, we can find $k$ if we know $[A]_0$. However, since we're looking for $[A]_0$, we use the given concentration at 15.6s (0.36M) to find it. Rearranging the equation to solve for $[A]_0$ and using the given data, we calculate the initial concentration, which matches the option provided.

Consider the Second-Order Reaction AA → Products (Which Has a First