Explain activation energy in 12th class chemistry
Answers
Activation energy is the minimum amount of energy that is needed to start a chemical reaction. The activation energy is the difference between the energy of the reactants and the maximum energy (i.e. the energy of the activated complex).
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order to understand the concept of activation energy, it can be visualized as the magnitude of the energy barrier (or the potential barrier) which separates the minima of potential energy surfaces involving the initial and the final thermodynamic state of the system.
This concept was first introduced by Swedish Chemist Svante August Arrhenius in the year 1889. A graph illustrating the activation energy of a reaction is provided below.
Activation Energy
It can be noted that the activation energies of different reactions vary. This energy requirement can be affected by the temperature of the system and also by the presence of a catalyst.
Temperature Dependence of the Rate of Reaction
From the Arrhenius equation, the following equation can be considered in order to calculate the activation energy of a system:
k=Ae−EaRT
Wherein: k refers to the rate constant, T refers to the absolute temperature, R is the universal gas constant, and A refers to the frequency of correctly oriented collisions. Ea is the activation energy as discussed earlier.
Negative Activation Energy
A negative value of activation energy is found in the Arrhenius equations of reactions wherein the rate of reaction slows down due to an increase in temperature.
In general, reactions which show a negative value for the activation energy are barrierless reactions which involve the capture of molecules in a given potential well.
An increase in the temperature for these reactions results in a reduction in the probability of the colliding molecules to capture each other.
