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For the reaction 2A + B → C, the values of initial rate at different reactant concentrations are given in the table below. The rate law for the reaction is:
[A] (mol L⁻¹) | [B] (mol L⁻¹) | Initial Rate (mol L⁻¹ s⁻¹)
0.05 | 0.05 | 0.045
0.10 | 0.05 | 0.090
0.20 | 0.10 | 0.72
- Rate = k [A][B]
- Rate = k [A][B]²
- Rate = k [A]² [B]²
- Rate = k [A]² [B]
Correct answer: Rate = k [A][B]²
Solution
Doubling [A] (B fixed) doubles the rate -> first order in A. From row 2 to 3, [A] doubles (x2) and [B] doubles while rate increases 8-fold; A accounts for x2, so B accounts for x4 -> second order in B. Rate = k[A][B]^2.
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