2A + B gives 3C + D. Which of the following does not express the reaction rate?
- A. -d[B]/dt
- B. d[D]/dt
- C. -1/2 d[A]/dt
- D. -1/3 d[C]/dt
Explanation
Rate is expressed as the change in concentration divided by the coefficient, with a minus sign for reactants because they are being consumed and a plus sign for products because they are being formed. C is a product, so its term must be positive, and writing it with a minus sign makes the expression wrong. The other three all give the same positive rate.