Which of the following is the correct rate law for the reaction between HCl and Na2S2O3, assuming the reaction is first order with respect to each reactant?

• A. rate = k[HCl]^2[Na2S2O3]^2
• B. rate = k[HCl]^2[Na2S2O3]
• C. rate = k[HCl][Na2S2O3]
• D. rate = k[HCl][Na2S2O3]^2

Answer: (C)

Verified step by step guidance

1. Understand that the rate law expresses how the rate of a reaction depends on the concentration of reactants, typically in the form \(\text{rate} = k[\text{A}]^m[\text{B}]^n\), where \(m\) and \(n\) are the orders with respect to each reactant.
2. Given that the reaction is first order with respect to each reactant, this means the exponent for each reactant's concentration in the rate law is 1.
3. Write the rate law using the given orders: since both HCl and Na2S2O3 are first order, the rate law is \(\text{rate} = k[\text{HCl}]^1[\text{Na}_2\text{S}_2\text{O}_3]^1\).
4. Simplify the expression by removing the exponents of 1, resulting in \(\text{rate} = k[\text{HCl}][\text{Na}_2\text{S}_2\text{O}_3]\).
5. Compare this expression to the options provided to identify the correct rate law.