Question Video: Identifying Which Statement Best Defines the Rate of a Chemical Reaction Science • Third Year of Preparatory School

Video Transcript

Which of the following statements best defines the rate of a chemical reaction? (A) The measure of change in the concentration of the reactants or products per unit of time. (B) The difference in mass between the reactants and the products. (C) The final concentration of the products following a chemical reaction. (D) The speed at which particles need to move in order to successfully collide. (E) Time at which the concentration of the products and reactants are equal.

The rate of a chemical reaction tells us its speed, in other words whether the reaction will be fast or slow. To define this quantity, we should know that a rate in general is a change in some quantity per unit time. For example, the rate or speed of a car is the change in distance per unit time. But during a chemical reaction, it’s not the distance that’s changing. It’s the amount of the reactants and products. Over time, the amount of reactants decrease as they’re used up. And the amount of the products increases as they’re formed. We can measure this amount as a volume, a mass, or a concentration. But the most common measure is probably the concentration of the reactants and products. Given what we’ve talked about, answer choice (A) seems to best define the rate of a chemical reaction: the measure of change in the concentration of the reactants or products per unit of time.