Which method is most commonly used to deduce the rate law of a reaction from experimental data showing how concentration changes over time?

• A. Analyzing initial rates for different reactant concentrations
• B. Determining the enthalpy change of the reaction
• C. Calculating the molar mass of the reactants
• D. Measuring the equilibrium constant at various temperatures

Answer: (A)

Verified step by step guidance

1. Understand that the rate law expresses the relationship between the reaction rate and the concentrations of reactants, typically in the form \(rate = k[A]^m[B]^n\) where \(k\) is the rate constant and \(m\), \(n\) are the reaction orders.
2. Recognize that to determine the rate law experimentally, you need to find how the rate depends on the concentration of each reactant, which requires measuring the reaction rate at different initial concentrations.
3. Focus on the method of analyzing initial rates: by measuring the initial rate of reaction (right at the start, before concentrations change significantly) for various initial concentrations of reactants, you can isolate the effect of each reactant's concentration on the rate.
4. Use the initial rate data to compare how changes in concentration affect the rate, allowing you to deduce the reaction orders \(m\) and \(n\) by observing proportional changes in rate relative to concentration changes.
5. Note that other options like determining enthalpy change, molar mass, or equilibrium constants do not provide direct information about the rate law, as they relate to thermodynamics or physical properties rather than kinetics.