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The limitations of balanced chemical equation is the speed of a chemical reaction. We may get the following information from a well balanced chemical equation:

Rate of reaction is the number of moles of product formed or reactants consumed per unit time. The mathematical statement is as follows:

The major idea that this theory postulates is that when different molecules collide, one of the molecules will receive energy from the other which will then raise the potential energy of the receiving molecule.

For a chemical reaction to occur, there must first be collision between the particles of the reactants. However, not all collision ever lead to a successful chemical reaction, only a small fraction of them (about one in 10¹⁴ collisions) can do so. These are called effective collisions.

The reason for the acquiring of minimum energy by the particles of the reactants is because reactions involve the breaking of bonds. The breaking of bonds is made possible only if the reactant particles collide with sufficient energy. The minimum energy which the reactant particles must have for reaction to occur is called activation energy.

Every reaction has its own energy of activation. Any reaction with a low activation energy will take place spontaneously even at low temperature. Whereas, a reaction with a high activation energy can only take place if extra energy {in the form of heat, electricity or light} is supplied.

The frequency with which the particles collide is dependent on the concentration of the particles or the number of particles per unit volume. If the particles are crowded, the more likely they will collide frequently and react with one another. Hence, when there is an increase in the concentration of the reactants, there will be a corresponding increase in the reaction rate and vice versa.

In this experiment, iodine is liberated when H₂O₂ {Hydrogen peroxide} is added to potassium iodide solution, KI that is acidified with tetraoxosulphate(VI) acid.

The dark blue coloration that is soon observed develops fastest in the reaction mixture with the highest concentration of reactants. The time for the colour development becomes progressively longer as the concentration of the reactants decreases, such that the colour development is slowest in the reaction mixtures that have the lowest concentration of reactants.

Another experiment that demonstrates the effect of concentration on the rate of chemical reaction is the reaction between magnesium and dilute hydrochloric acid. Effervescence that occurs in this experiment when magnesium is added to HCl proceeds at a faster rate and is completed in a short time. If it proceeds at a slower rate, then the reaction will be completed in a longer time. (See Fig.1).

Therefore, the rate of reaction is inversely proportional to the duration of the effervescence and by extension, the production of hydrogen gas during the experiment (that is, the reaction between Mg and HCl).