Factors Influencing Rates Of Chemical Reactions

Factors influencing Rates of Chemical reactions There are various factors that effect the rate of a reaction. These are 1. 2. 3. 4. 5. 6. 7.

Concentration of reactants Effect of Pressure Effect Temperature Effect Surface Area Effect Stirring Effect Catalyst Effect radiation

Effect of Concentration If the concentration of any reactant in a solution is increased, the rate of reaction increases. This is because; Increase in the concentration, increases the probability of a collision between reactant particles because more of them are presents in the same volume and so it increases the chance of a collision to form products. In general, increasing the concentration of reactant A or B will increase the chance or frequency of a successful collision between them and increase the speed of product formation. Effect of Pressure If one or more of the reactants is a gas, then increasing pressure will effectively increase the concentration of the reactant molecules and speed up the reaction. On increasing pressure, collision among the molecule increases and due to this speed of the reaction will also increase. Effect of Temperature When gases or liquids are heated the particles gain kinetic energy and move faster. The increased speed increases the (frequency)

of collision between reactant molecules and the rate increases. This effect is observed for both exothermic and endothermic reactions. A general approximate rule for the effect of temperature on reaction rates is that the reaction rate for most of the chemical reactions becomes almost double, for every 10 0C rise in temperature.

Effect of Surface area If a solid reactant or a solid catalyst is broken down into smaller pieces the rate of reaction increases. The increase in the speed is because; the smaller pieces of the same mass of solid have a greater surface area as compared to larger pieces of the solid. Therefore, there is more chance that a reactant particle will hit the solid surface and react. Effect of Stirring Stirring the mixture is an important rate factor. If the reacting mixture is not stirred ‘evenly’, the reactant concentration in solution becomes much less near the solid, which tends to settle down at the bottom of the container Therefore, at the bottom of the container the reaction prematurely slows down.It changes the overall rate measurement and making the results uneven and inaccurate. Effect of the nature of reactants and products As we know that during a chemical reaction old bonds are broken and new bonds are formed .The reactivity of a substance can, therefore, be related to the ease with which the specific bonds are broken or formed and the number of such bonds involved. E.g. the oxidation of nitric oxide to nitrogen dioxide takes place rapidly while oxidation of carbon monoxide to carbon dioxide takes place slowly

In the above examples, the reacting species in both the reactions appear to be same but differ in their reaction rates. Effect of presence of Catalyst A catalyst is a substance that influences a rate of a reaction without undergoing any change itself. Presence of certain catalysts increases the rate of reaction. For example H2 and O2 don’t react at room temperature but in the presence of finely divided platinum (catalyst) the reaction becomes quite vigorous. Effect of Radiation In some cases, the rate of chemical reaction increases by the use of certain radiations. This is because photons of the radiations possess sufficient energies to break certain bonds in the reactants. For example reaction between hydrogen and chlorine it is very slow in the absence of light. But in the presence of light, the rate of reaction is very fast.