Nature and state of the reactant: We know that a chemical reaction involves breaking of certain existing bonds of the reactant and forming new bonds which lead to the product.
The net energy involved in this process is dependent on the nature of the reactant and hence the rates arc different for different reactants. Let us compare the following two reactions that we carried out in volumetric analysis.
1. Redox reaction between ferrous ammonium sulphate (FAS) and KMnO4
2. Redox reaction between oxalic acid and KMnO4
The oxidation of oxalate ion by KMnO4 is relatively slow compared to the reaction between KMnO4 and Fe . In fact heating is required for the reaction between KMnO4 and Oxalate ion and is carried out at around 60°C. The physical state of the reactant also plays an important role to influence the rate of reactions. Gas phase reactions are faster as compared to the reactions involving solid or liquid reactants.
For example, reaction of sodium metal with iodine vapours is faster than the reaction between solid sodium and solid iodine. Let us consider another example that we carried out in inorganic qualitative analysis of lead salts.
If we mix the aqueous solution of colorless potassium iodide with the colorless solution of lead nitrate, precipitation of yellow lead iodide take place instantancously, whereas if we mix the solid lead nitrate with solid potassium iodide, yellow coloration will appear slowly.
