Which experimental method is commonly used to determine the rate law by varying one reactant at a time and measuring initial rates?

Which experimental method is commonly used to determine the rate law by varying one reactant at a time and measuring initial rates?

• A. Initial-rate method
• B. Titration curve method
• C. Integrated-rate method
• D. Global-fit method

Answer: (A)

The key idea here is determining how the rate depends on each reactant’s concentration by changing one reactant at a time and looking at the initial rate. This is the initial-rate method. By holding all other reactants constant and varying one concentration, you can infer the reaction order with respect to that reactant from how the rate changes. For example, if doubling the concentration of a reactant doubles the initial rate, the order with respect to that reactant is first order; if the rate goes up by a factor of four, it’s second order, and so on. Measuring at the initial moment avoids complications from changing concentrations as the reaction proceeds. This approach is used specifically because it gives direct information about how each reactant contributes to the rate, in a straightforward way. Other methods don’t match this setup: one method analyzes how concentration changes over time to fit an integrated rate law for a given order, rather than identifying the orders by varying concentrations one at a time; another concept uses global fitting of many data sets to determine a rate law, which is a broader statistical approach rather than the one-at-a-time initial-rate comparison.

The key idea here is determining how the rate depends on each reactant’s concentration by changing one reactant at a time and looking at the initial rate. This is the initial-rate method. By holding all other reactants constant and varying one concentration, you can infer the reaction order with respect to that reactant from how the rate changes. For example, if doubling the concentration of a reactant doubles the initial rate, the order with respect to that reactant is first order; if the rate goes up by a factor of four, it’s second order, and so on. Measuring at the initial moment avoids complications from changing concentrations as the reaction proceeds.

This approach is used specifically because it gives direct information about how each reactant contributes to the rate, in a straightforward way. Other methods don’t match this setup: one method analyzes how concentration changes over time to fit an integrated rate law for a given order, rather than identifying the orders by varying concentrations one at a time; another concept uses global fitting of many data sets to determine a rate law, which is a broader statistical approach rather than the one-at-a-time initial-rate comparison.