If rate = k [A]^2 [B], what is the rate factor when you double [A] and [B] simultaneously?

• A. 4
• B. 2
• C. 8
• D. 16

Answer: (C)

The rate depends on concentrations as rate = k [A]^2 [B]. When you double both [A] and [B], the rate scales by (2)^2 for A because A is squared, giving a factor of 4, and by (2)^1 for B because B is first order, giving a factor of 2. Multiply these effects: 4 × 2 = 8. So the rate becomes eight times the original rate. The requested rate factor is 8.