Determination of the Rate of a Chemical Reaction

Introduction to the Rate of a Chemical Reaction

Determination of the rate of a chemical reaction entails the measurement of the concentration of reactants or products at regular time intervals as the reaction proceeds. When the reaction goes on, the concentrations of reactants decrease as well as those of products boost. The rate of a reaction, as a result, is shown in regard to the rates at which the concentration alters.


The change in concentrations of reactants or products can be figured out by both physical and chemical techniques depending upon the kind of reactants or products involved in the chemical reaction.

  1. Physical Methods

Several of the techniques made use of for this purpose are the following:

  • Spectrometry

This method applies if a reactant or product takes in ultraviolet, visible or infrared radiation. The rate of reaction can be determined by measuring the amount of radiation absorbed.

  • Electrical Conductivity Method

The rate of reaction entailing ions can be examined by electrical conductivity method. The conductivity of such a solution depends upon the rate of changes of concentration of the reacting ions or the ions formed during the reaction. The conductivity will be proportional to the rate of changes in the concentration of such ions.

  • Dilatometric Approach
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This method serves for those reactions, which involve tiny volume changes in solutions. The volume change is directly proportional to the reaction.

  • Refractometric Technique

This method is applicable to reactions in solutions, where there are changes in refractive indices of the materials taking part in the chemical reactions.

  • Optical Rotation Approach

In this method, the angle whereby plane polarized light is revolved by the reacting mixture is determined by a polarimeter. The level of rotation determines the concentration of an optically energetic compound. If any of the species in the reaction mixture is optically energetic, after that this technique can be followed to find out the rate of reaction.

  1. Chemical Method

This is especially suitable for reactions in solution. In this method, there is a chemical analysis of a reactant or a product that is involved in a chemical reaction. The acid hydrolysis of an ester (ethyl acetate) in the existence of a small amount of acid is one of the best examples.

CH3COOC2H5 (l) +H2O (l) à CH3COOH (l) + C2H5OH (l)

In the case of hydrolysis of an ester, the solution of ester in water and the acid functioning as a catalyst are enabled to react. After a time, a sample reaction mixture is taken out by a pipette and run into 4 times its volume of ice-cold water. The dilution as well as cooling stops the reaction. The acid formed is titrated against a common alkali, let’s say NaOH, making use of phenolphthalein as an indicator.

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The analysis is repeated at numerous time intervals after the beginning of the reaction. This would certainly offer a detail regarding the changes in concentration of acetic acid created during the reaction at different time intervals.

The incline of the curve at any kind of factor will offer the rate of reaction. At first, the rate of reaction is high however it reduces with the flow of time. When the curve ends up being horizontal, the rate of reaction ends up being zero.


If we outline the chart for decreasing concentrations of CH3COOC2H5, after that, dropping curves are acquired. If we have any kind of lab method to record the changing concentration of ester or alcohol, we can measure the rate of reaction.

This is a pseudo-first-order reaction. Actually, water being in large excess in comparison to ester does not affect the rate and we assume that water is not taking part in the reaction.

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