What is a reaction rate?

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t-nez | High School Teacher | (Level 3) Associate Educator

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A reaction rate is the speed at which a chemical reaction progresses. It can be expressed in terms of disappearance of any reactant (change in concentration/change in time) or appearance of any product. The rate of a chemical reaction is described by a rate law, a mathematical expression that includes factors for the concentrations of all reactants affecting the rate, each raised to the power by which they affect the rate. for example, for a reaction with reactants A and B might have the following rate law:

rate = k[A][B]^2

k is a constant unique to that temperature, [A] is the molar concentration of reactant A and [B] is the molar concentration of reactant B. According to this rate law the rate is directly dependent on the concentration of A and depends on the square of the concentration of B. So if you double A's concentration the rate will double, but if you double B's concentration the rate will quadruple. The exponents of [A] and [B] are determined experimentally by varying concentrations of reactants and measuring the rate.

Some factors that usually increase the rate of a chemical reaction are:

1. Increasing the concentration of any reactant in the rate law

2. Using a catalyst

3. Shaking, stirring or agitating

4. Increasing the surface area of a reactant (powdered vs. a solid chunk)

5. Raising the temperature