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Chemistry > Chemical Reactions and Equations > Order of Reaction – Example and How to Determine it?
Chemical Reactions and Equations

Order of Reaction – Example and How to Determine it?

Introduction to Order of Reaction 

The order of reaction provides an indication of how changing the concentration of the reactant will affect the reaction’s speed. Its determination carries important applications in chemistry.

It explains the relationship between the rate of a chemical reaction‘s rate and the species concentration in it. Students can explore more about order of reaction here.

order of reaction

What is Order of Reaction?

The order of reaction is the power dependence of the rate on the concentration of reactants. Therefore, for a first order reaction to take place, the dependence of the rate is certainly on the concentration of a single species.

A second order of reaction is the one where the dependence of the rate is certainly on the square of the concentration of a single reactant. Furthermore, it also refers to the combined first-order dependence on the concentrations of two different reactants.

One must understand that the order of reaction is a parameter which is experimentally determined. Furthermore, it can take on a fractional value. This is certainly different from the molecularity of the reactions.

How to Find the Order of Reaction?

There is a relation between the rate of reaction and the concentration of a reactant by the rate constant. Furthermore, its representation is by the letter K. Moreover, there is a constant change in the rate as the temperature changes.

However, the rate remains the same when change occurs but only in the concentration. The reaction which takes place at constant pressure and temperature, for this the rate equals the rate constant times the concentration of reactants to the power. Most noteworthy, this power is of the order of each reactant.

The general formula is below:

Rate of reaction = kAxByCz…, where A, B, C… are certainly the concentrations of each reactant. Also, x, y, z… happen to be orders of the individual reactions.

For one interested in the overall order of reaction, it is x + y + z +…. For example, for the three first-order reactions of three reactants, the overall order of reaction is certainly three. Also, for the two second-order reactions of two reactants, the overall order of the reaction happens to be four.

Examples of Orders of Reaction

The iodine clock reaction rate is quite easy to measure. This is because the solution in the reaction container turns blue when reaction is completed. Moreover, this time to turn blue is proportional to the reaction’s rate.

Consider an example of doubling the concentration of a reactant. This makes the solution blue in roughly half the time. Hence, one can see that the rate of reaction has certainly doubled.

One important order of reaction is a zero-order reaction. For a zero order reaction, change in concentration makes no difference.

Furthermore, decomposition reactions which include the decomposition of nitrous oxide are probably zero-order reactions. This is because the substance decomposes independently of the concentration.

Solved Question for You

Q1. Which of the following statements is not true with regards to the order of reaction?

A. It provides an indication of how changing the concentration of the reactants will affect the reaction’s speed
B. For a first order reaction to take place, the dependence of the rate is certainly on the square of the concentration of a single reactant
C. It is the power dependence of the rate on the concentration of reactants
D. It is a parameter which is experimentally determined

A1. The correct answer is option B.  This is because, the correct statement is “for a first order reaction to take place, the dependence of the rate is certainly on the concentration of a single species.”

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