Which of the following expressions correctly shows how the rate of a reaction depends on the concentrations of its reactants?

• A. rate = k[A]^m[B]^n
• B. rate = k[A] - [B]
• C. rate = k[A] + [B]
• D. rate = k[A][B]/[C]

Answer: (A)

Verified step by step guidance

1. Understand that the rate of a chemical reaction typically depends on the concentrations of the reactants raised to some powers, which are called the reaction orders with respect to each reactant.
2. Recall the general rate law expression for a reaction involving reactants A and B: \(\text{rate} = k [A]^m [B]^n\), where \(k\) is the rate constant, and \(m\) and \(n\) are the reaction orders determined experimentally.
3. Note that the rate law is a product of the concentrations raised to their respective powers, not a sum or difference of concentrations.
4. Recognize that expressions like \(\text{rate} = k[A] - [B]\) or \(\text{rate} = k[A] + [B]\) do not correctly represent how reaction rates depend on concentrations because rates are not calculated by adding or subtracting concentrations.
5. Also, understand that dividing by the concentration of a reactant, as in \(\text{rate} = \frac{k[A][B]}{[C]}\), is not a standard form of a rate law unless specifically determined by the reaction mechanism, which is uncommon and not given here.