Concentration Changes Over Time

The Effect of Concentration on Reaction Rate

The rate of a chemical reaction can often be changed by altering the concentrations of the reactants.
As concentration increases, the number of particles per unit volume will also increase. This results in a higher probability of successful collisions per unit time, consequently speeding up the reaction.
On the other hand, if the concentrations of the reactants are reduced, the frequency of successful collisions decreases, leading to a slower reaction rate.

Reaction rate is governed by the collision theory, which states that for a reaction to occur, reactant particles must collide with sufficient energy and correct orientation.
When concentration increases, more particles are available for collisions, therefore increasing the likelihood of frequent and successful collisions.

The relationship between concentration and reaction rate is usually expressed in the rate law equation: rate = k[A]^m[B]^n.
Here, ‘rate’ is the speed of the reaction, ‘k’ is the rate constant, ‘A’ and ‘B’ are the reactants and ‘m’ and ‘n’ are orders of reaction with respect to the reactants A and B.
When the concentrations of the reactants are doubled, the rate of reaction will increase by a factor determined by the order of reaction.

For zero order reactions, changes in reactant concentration have no impact on the rate of reaction. This suggests that the reaction rate is independent of the concentration of that particular reactant.
In first order reactions, doubling the concentration of that reactants results in a two-fold increase in the rate of reaction.
For second order reactions, doubling the concentration results in a four-fold increase in the reaction rate. This indicates that the rate of reaction is proportional to the square of the reactant concentration.

In kinetic studies, it’s often necessary to calculate the change in concentration of a reactant over time.
It’s essential to understand how to read and interpret a concentration-time graph. A straight line on such a graph indicates a zero order reaction, while a curve that becomes less steep over time signifies a first order reaction.
The rate constant ‘k’ can be calculated from the slope of these graphs.