From data: Doubling [A] increases rate by 3x; tripling [A] increases rate by 6x. Approximate the reaction order n?

• A. Approximately 1.6
• B. Approximately 2
• C. 0
• D. 3

Answer: (A)

The rate law for a reaction that depends on a single reactant A is rate = k [A]^n. When you double the concentration, the rate scales by 2^n. Since the rate increases by a factor of 3 when [A] is doubled, you have 2^n = 3, so n = log(3)/log(2) ≈ 1.585, about 1.6.

You can check with the tripling data: 3^n should give a factor of 6, so n = log(6)/log(3) ≈ 1.631, also near 1.6. The two estimates agree, pointing to a fractional order.

Therefore, the approximate reaction order with respect to A is about 1.6, meaning it lies between first and second order. Fractional orders often arise from complex reaction mechanisms where the dependence on concentration isn’t simply an integer power.