For the reaction A →  B, the rate constant is 0.0837 M^–1•sec^–1. How long would it take for [A] to decrease by 85%?

• A. 0.0211 s
• B. 1.94 s
• C. 179 s
• D. 0.677 s

Answer: (D)

Verified step by step guidance

1. Identify the order of the reaction. Since the rate constant is given in units of M^-1•s^-1, this indicates a second-order reaction.
2. For a second-order reaction, the integrated rate law is: $\frac{1}{/}=\; kt\; +\frac{1}{/}$, where At is the concentration at time t, A0 is the initial concentration, and k is the rate constant.
3. Determine the final concentration At after a decrease of 85%. If the initial concentration A0 is 1 M, then At = 0.15 M.
4. Substitute the known values into the integrated rate law: $\frac{1}{/}=\; 0.0837t\; +\frac{1}{/}$.
5. Solve the equation for t to find the time it takes for the concentration to decrease by 85%.