Detail, with appropriate scientific theory, the five main factors that affect the rate of a reaction

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Andrew Roberts

Detail, with appropriate scientific theory, the five main factors that affect the rate of a reaction

        A chemical reaction involves the breaking of bonds within the reactants and the creation of bonds to form products. Different bonds have different strengths so the energy required for various reactions to occur is different. The rate at which a reaction progresses is controlled by five main factors: - concentration, pressure, temperature, surface area and catalysis.

A reaction profile is a graph that shows the energy changes involved during a reaction against time. The basic structure for an exothermic reaction is: -

        The graph shows that in the intermediate transition stage the reactants have gained more energy from their original form, and then go on to another energy level as products. The graph shows the activation energy required and the energy released. For an endothermic reaction, the reaction profile is similar except the products finish on a higher energy level, thus showing that energy has gone into the reactants to form the products.

The collision theory is a theory used to explain rates of reaction. It is based on the simple context that for two particles to react they must collide, where only a fraction of the collisions occurring result in a reaction taking place. There two factors affecting this: -

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  • The molecules must approach each other in the correct orientation (steric factor)
  • The molecules must have a minimum amount of energy (activation energy)


If the reactants are gases, when the pressure is increased there will be more moles of each gas per unit area than at lower pressures: -

 

                                     

This shows that as the molecules move around they will be far more likely to collide with another molecule at high pressure than at low pressure. Collision theory says ...

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