Science Articles

INTRODUCTION TO THE ARRHENIUS EQUATION

The Arrhenius equation is a formula for the temperature dependence of reaction rates.

Everyone knows that the chemical reactions occur more speedily at higher temperatures. For example, milk turns sour faster at room temperature than in a refrigerator or the eggs hard boil more quickly at the sea level than at that of the mountains. The reason for this is that the thermal energy relates direction to the motion at molecular level.

With increase in temperature, the molecules move faster and collide even more vigorously. This increases the rearrangements and bond cleavages. It is undetermined whether it is caused due to collision theory or transition theory or some other, but chemical reactions do take place faster at higher temperatures when compared to the lower temperatures.

It was known by everyone by 1890, that the higher temperatures doubles up the rate for the 10 degree rise in temperature but no one could explain why. In 1899, Svante Arrhenius (1859-1927), a Swedish chemist, combines the Boltzman distribution law and the concepts of the activation energy into a chemical relationship which said-

K = A e –

Where A is the pre-exponential factor or the frequency factor which specifically relates to the collision of molecules

RT is the average kinetic energy (R is the gas constant and T is the absolute temperature at which the reaction is taking place)

Ea is the activation energy (it is known as the threshold energy that the reactants should reach before they can reach the transition state)

K is the chemical reaction rate constant

This equation was developed for characterising the temperature-dependent reactions. The Arrhenius equation has been widely used in the variety of fields like the material engineering, civil engineering and chemistry. The Arrhenius equation is said to the formula for the dependency of temperature on the rate of reactions.

 

IMPLICATIONS OF THE ARRHENIUS EQUATION

The rate constant of the reaction increases exponentially with the decrease in the activation energy. Since the rate of the reaction is directly proportional to the rate constant of the reaction, there is increase in the rate exponentially. Since the reaction with small activation energy doesn’t need much energy for reaching the transition state, the reaction can proceed faster when compared to the one with larger activation energy.

The Arrhenius equation implies that the rate of the un-catalysed reaction gets more affected by the temperature than the catalysed one. This happens owing to the fact that the un-catalysed reaction has higher activation energy than the activation energy of the catalysed reaction.