Calculate the average rate of reaction from the change in concentration over time, or solve a rate law for the reaction rate or rate constant k.

Species and stoichiometry

Balanced-equation coefficient; blank uses 1.

Rate of Reaction Formula

This two-reactant power-law model calculates reaction rate from experimentally determined orders and a rate constant with matching concentration and time units. It is not a universal rate law.

v = k × [A]x × [B]y
  • Where v is the rate of reaction
  • A is the concentration of species A
  • B is the concentration of species B
  • x is the order of reaction with respect to A
  • y is the order of reaction with respect to B
  • k is the rate constant

To calculate the rate of reaction, raise the concentration of species A to the order of reaction concerning A, then multiply the result by the concentration of species B to the order of reaction concerning B. Finally, multiply the result by the rate constant.

Rate of Reaction Definition

At constant volume, a reaction rate can be found from a reactant concentration decrease or product concentration increase divided by elapsed time and the species’ positive balanced-equation coefficient. This average-rate interpretation assumes fixed stoichiometry without appreciable intermediate accumulation; a single tracked species is sufficient.

Rate of Reaction Example

How to calculate a rate of reaction?

  1. First, determine the concentration of species A and B.

    Calculate the initial concentrations of both species.

  2. Next, determine the order of reactions.

    Calculate the order of reactions with respect to A and the order with respect to B.

  3. Next, determine the rate constant.

    Calculate or determine the rate constant.

  4. Finally, calculate the rate of reaction.

    Calculate the rate of reaction using the equation above.

FAQ

What is a rate of reaction?

For a fixed-stoichiometry reaction at constant volume, reaction rate is a species concentration-change rate divided by its stoichiometric coefficient, with a negative sign for a consumed reactant. An interval measurement gives an average rate.