Which is the Best Definition of Activation Energy

Which is the Best Definition of Activation Energy

Activation energy is often studied under physical chemistry and it is a very important concept related to chemical kinetics in JEE. The term Activation Energy was first used past a Swedish scientist named Svante Arrhenius in the year 1889. Today, we learn about this concept equally it helps us understand the energy requirements for a chemic reaction which further gives us control over our actions and the surround.

Almost all the chemical reactions require some activation free energy to go forrard. Therefore, information technology is important for students to know what is activation energy. We shall learn more well-nigh this concept in this lesson.

Tabular array of Content

  • Activation Energy Definition
  • Factors Affecting Activation Energy
  • Activation Free energy Examples
  • Catalysts
  • Activated Complex
  • Activation Free energy Formula

Activation Free energy Definition

Activation free energy is defined as the minimum corporeality of extra energy required by a reacting molecule to get converted into product. It tin can also be described as the minimum corporeality of energy needed to activate or energize molecules or atoms so that they can undergo a chemic reaction or transformation.

What is the SI Unit of measurement of Activation Energy?

Activation energy is denoted by Ea. It is commonly measured in joules (J) and or kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).

Factors Affecting Activation Energy

Activation energy depends on 2 factors.

1. Nature of Reactants

In the case of ionic reactant, the value of (Eastwarda) will exist depression because at that place is an attraction between reacting species. While in the case of covalent reactant the value of Ea
will exist high because energy is required to break the older bonds.

Also Read:
Chemic Kinetics

2. Effect of Catalyst

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Positive catalyst provides such an alternating path in which the value of Easta
will be low, while the negative goad provides such an alternate path in which the value of Ea
volition be loftier.

Activation energy does non depend upon the temperature, pressure level, book, concentration, or coefficients of reactant.

Activation Energy Examples

Exothermic Reaction

Exothermic Reaction

Activation energy for Forward reaction (Easta)f

Activation energy for Forward reaction (Eastwarda)b

< (Easta)b

> (ROR)b

△H = (Ea)f
– (Eastwarda)b

△H = -ve value

(Due easta)f
= △H Only one can be possible for Exothermic Reaction

> △H

< △H

Read More than:Exothermic Reaction

Endothermic Reaction

> (Due easta)b

< (ROR)b

△H = (Ea)b
– (Easta)f

△H = +ve value

> △H (Ever )…………universal

Endothermic Reaction

Read More:Endothermic Reaction


A catalyst is a chemical substance that either increases or decreases the rate of a chemic reaction. In the case of activation energy, a goad lowers it. All the same, the energies of the original reactants remain the aforementioned. A catalyst only alters the activation free energy.

Types of Catalysts

Positive Catalysts

A goad that helps to increase the rate of reaction or which support the reaction to carry out quickly is called a positive goad. Such goad decreases activation energy by accepting a smaller path, so the rate of reaction is increased.

Positive Catalysts

Negative Catalysts (Inhibitors)

A catalyst that decreases or retards or helps in slowing downwardly the charge per unit of reaction is called negative catalysts.

Negative Catalysts (Inhibitors)

It is considering a negative catalyst increases activation free energy by taking a longer alternative path.

Points to Recollect

Forward Reaction:
Those reactions in which the product formed are produced from reactants

Astern Reaction:
These are those reactions when reaction goes from products to reactants.

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Activated Complex

When reactant molecules collide with each other at its highest free energy point, an intermediate is formed which remains in equilibrium with the main reactant. If this intermediate complex has an energy equal to or greater than the Threshold Energy and so it will be converted into a production.

Activated Complex

Activation Free energy Formula

The formula used to observe the value of Activation Free energy, Easta

K = Ae-Due east


One thousand = Rate Abiding

A = Arrhenius Constant

= Activation Energy

R = Gas abiding = eight.34J/K/mol

=viii.314/1000 KJ/Thou/mol

= 2 cal/K/mol

= 0.0821 lit atm/K/mol

K = Ae-E

Taking log on both sides

ln One thousand = ln A – (Ea

/RT)ln eastward

2.303 log K = two.303 log A – Ea/RT

log Grand = log A – Due easta

Solved Examples Related To Activation Energy

1. The rate constant of a 1st lodge reaction
increases from 3 × 10
to 8× ten-2
when the temperature changes from 310K to 330K. Calculate the activation energy (Ea)?


Given grandii
= 8× 10
-2, kone
= iii × 10-2, Tone=310K,T2


\(\brainstorm{array}{l}log \frac{k_{1}}{k_{2}} = \frac{E_{a}}{2.303 R}\left ( \frac{1}{T_{ane}}-\frac{i}{T_{two}} \right )\cease{array} \)

\(\begin{array}{l}log\frac{eight\times ten^{-two}}{3\times ten^{-ii}} = \frac{E_{a}}{2.303 R}\left ( \frac{1}{310} -\frac{1}{330}\right )\end{array} \)

\(\brainstorm{array}{l}log 2.66 =\frac{E_{a}}{2.303 R}(1.95503\times 10^{-4})\end{array} \)

\(\begin{array}{50}0.4249 = \frac{E_{a}}{2.303\times 8.314}\times (i.95503\times 10^{-04})\stop{assortment} \)

\(\brainstorm{array}{l}0.4249 = \frac{E_{a}}{19.147}\times (i.95503\times 10^{-04})\terminate{array} \)

\(\brainstorm{assortment}{l}0.4249 = one.02106\times 10^{-5}\times E_{a}\stop{array} \)


= 41,613.62 J/mole

= 41.614 kJ/mol

two. The charge per unit constant of the first-order reaction raises from 3
Ten 10

 to 5×10

when the temperature change from 300K to 310K. Calculate the activation energy?


Given g2
= 3 × 10-2, k1
= 5 × x-2, Ti= 300K, T2
= 310K

\(\begin{assortment}{l}log \frac{k_{1}}{k_{2}} = \frac{E_{a}}{2.303 R}\left ( \frac{one}{T_{1}}-\frac{ane}{T_{2}} \right )\end{assortment} \)

\(\begin{assortment}{50}log\frac{5\times ten^{-ii}}{three\times 10^{-2}} = \frac{E_{a}}{2.303 R}\left ( \frac{1}{300} -\frac{one}{310}\right )\end{array} \)

\(\begin{array}{fifty}log ane.66 =\frac{E_{a}}{2.303 R}(1.07526\times 10^{-04})\terminate{array} \)

\(\begin{array}{l}0.2218 = \frac{E_{a}}{2.303\times eight.314}\times (one.07526\times 10^{-04})\end{array} \)

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\(\begin{array}{fifty}0.2218 = \frac{E_{a}}{19.147}\times (1.07526\times 10^{-04})\terminate{assortment} \)

\(\brainstorm{array}{l}0.2218 = 5.6158\times 10^{-6}\times E_{a}\finish{assortment} \)


= 39,495.7 J/mole

= 39.495 kJ/mol

three.  The first order reaction has rate constant of 2.0×ten-2
and 6.0×10
at 0C and 30
C. Calculate the activation free energy of the reaction?


Given g

= 6 × ten

, thousand

= 2 × ten

, T
= 273K, T

= 303K

\(\brainstorm{array}{fifty}log \frac{k_{ane}}{k_{two}} = \frac{E_{a}}{2.303 R}\left ( \frac{ane}{T_{1}}-\frac{1}{T_{ii}} \correct )\end{array} \)

\(\begin{array}{50}log\frac{6\times 10^{-2}}{ii\times 10^{-2}} = \frac{E_{a}}{two.303 R}\left ( \frac{one}{273} -\frac{1}{303}\correct )\end{array} \)

\(\begin{array}{l}log 3 =\frac{E_{a}}{2.303 R}(3.6267\times 10^{-04})\end{array} \)

\(\begin{array}{fifty}0.4771 = \frac{E_{a}}{two.303\times 8.314}\times (3.6267\times ten^{-04})\finish{array} \)

\(\begin{assortment}{fifty}0.4771 = \frac{E_{a}}{xix.147}\times (three.6267\times 10^{-04})\terminate{array} \)

\(\brainstorm{array}{l}0.4771 = ane.8941\times 10^{-five}\times E_{a}\end{assortment} \)

Due east

= 25,188.74 J/mole

= 25.188 kJ/mol

Frequently Asked Questions – FAQs

What is the meaning of loftier activation free energy?

High activation free energy means loftier energy required to accept a successful collision between the particles, such as combustion. Even though combustion is an exothermic reaction, it requires heat because of the high activation free energy. The particle gains plenty energy from heat to overcome the barrier of activation free energy.

What is the difference between activation energy and energy?

Free energy is the chapters to exercise some work, whereas activation energy is the free energy needed to class the activated complex during the chemical reaction.

What is a negative catalyst?

A goad that decreases the reaction charge per unit is called a negative catalyst. The negative goad increases the activation energy of the reaction.

Does activation energy depend on temperature, pressure and other variables?

No, activation energy does not depend on any of the factors like temperature or pressure.

What is the SI unit of activation free energy?

The SI unit of measurement of activation energy is KJ/mol

Which is the Best Definition of Activation Energy

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