The rate of change in concentration of a reactant or product with time is called what?

• A. Instantaneous rate
• B. Rate Law
• C. Half-life
• D. Reaction rate

Answer: (D)

The rate at which concentration changes with time describes how fast reactants are consumed or products are formed in a reaction. This quantity is called the reaction rate. In practice, you can refer to the rate of appearance of a product or the rate of disappearance of a reactant, and these are linked by the reaction’s stoichiometry. The instantaneous rate is the rate at a specific moment, given by the slope d[concentration]/dt at that moment, while the average rate over a time interval is the change in concentration divided by the interval. The rate law is the equation that relates rate to concentrations and a rate constant, and half-life is the time needed for the concentration to fall to half. So, the term that best matches the description is the reaction rate.