When reactant concentration doubles, measured initial rate increases by a factor of four at constant temperature. Reaction order in that reactant is most nearly:
- (A)0.5
- (B)1
- (C)2
- (D)4
Show worked solution
Answer: (C)
For r proportional to C^n, 4=2^n, so n=2.
Rate ratios eliminate the constant rate coefficient.
The observed ratios are four and two.
FE Reference Handbook — Reaction Engineering: Rate Laws and Order
Why the other choices appear
- (A)Taking the square root of the rate ratio gives concentration ratio, not order.
- (B)First order would double rate when concentration doubles.
- (D)Using the rate factor directly as order ignores exponentiation.