of temperature on reaction rate Generally, the rate of a reaction increase with increasing temperature. However, there are very few exceptions. The magnitude of this increase in rate is different for different reactions. As a rough rule, for many reactions near room temperature, reaction rate tends to double when the temperature is increased by C Activity Let us understand the effect of temperature on reaction rate by doing this activity.
i. Take two test tubes, label them as A and B ii. Take ml of cold water in A, add a drop of phenolphthalein indicator and then add Magnesium granules. iii.
Repeat the above with ml of hot water in test tube B. B B B B B B Proper allignment Effective collission Products Reactants Reactants B B B B B B ineffective collision improper allignment Reactants Fig . - Orientation of reactants - schematic representation XII U7 kinetics - Jerald XII U7 kinetics - Jerald - - - - iv. Observe the two test tubes.
v. The observation shows that the solution in test tube B changes to pink colour and there is no such colour change in test tube A. That is, hot water reacts with magnesium according to the following reaction and there is no such reaction in cold water. Mg + 2H O Mg OH H ↑ vi.
The resultant solution is basic and it is indicated by phenolphthalein. A large number of reactions are known which do not take place at room temperature but occur readily at higher temperatures. Example: Reaction between H and O to form H O takes place only when an electric spark is passed. Arrhenius suggested that the rates of most reactions vary with temperature in such a way that the rate constant is directly proportional to e − E RT and he proposed a relation between the rate constant and temperature.
k=A E RT e − ....( ) Where A the frequency factor, R the gas constant, E a the activation energy of the reaction and, T the absolute