What do reaction rates measure?

Reaction rates specifically quantify how quickly a reactant is transformed into products within a chemical reaction. This measurement is typically expressed as the change in concentration of reactants or products over a designated period. By focusing on the speed of this conversion, B captures the essence of what reaction rates represent in the context of kinetics.

In terms of context, understanding reaction rates is crucial in various applications, such as determining the efficiency of catalysts, predicting the behavior of reactions under different conditions, and optimizing reaction conditions in industrial processes. The other options, while related to chemical processes, address different aspects. For example, the change in mass of reactants over time might be relevant, but it does not encompass the entire picture of the transformation that defines reaction rates. Similarly, measuring pressure changes or the amount of heat produced pertains more to thermodynamics and state changes, rather than directly measuring the rate of reaction progress. Thus, the focus on speed and conversion in the correct answer aligns precisely with the definition of reaction rates.