Question

Describe the method used to determine the rate of a reaction.

Answer 1

The rate of a chemical reaction can be measured by either observing the change in concentration of reactants or the change in concentration of products over time. There are several techniques through which this can be done:

1. pH Measurement: If there is a change in the concentration of H⁺ or OH⁻ ions during the reaction, this approach is employed. The pH changes as a result of these ions' concentration changing during the reaction. A continuous recording pH meter is used if the reaction is quick. It measures the pH instantly and produces a graph against time so that the reaction rate may be determined.
2. Change in Optical Activity: The rotation of plane-polarised light can be used to measure the concentration of isomers or stereoisomers in processes where they are either reactants or products. This is because the amount by which isomers and stereoisomers rotate the plane of polarised light varies. Therefore, there will be a commensurate shift in the observed rotation as the concentration of one isomer varies in relation to the other.
3. Change in Pressure: Gas reactions where the total number of moles of reactants and products differ are the main use for this technique. Changes in the amount of moles of the gases are directly correlated with changes in pressure. By measuring the change in pressure at different points during the reaction, one can observe the progress of such reactions.
4. Change in Conductance: The change in molar conductivity in reactions involving the production or consumption of an electrolyte gives an indication of the pace of the reaction. A conductometer can be used to measure the conductance of the solution, which will change in parallel with changes in the electrolyte concentration and provide an indication of the reaction's progress.