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

Also Read:
Chemic Kinetics

2. Effect of Catalyst

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

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

Activation Energy Examples

Exothermic Reaction

Activation energy for Forward reaction (East_a)_f

Activation energy for Forward reaction (Eastward_a)_b

(East_a)_f
< (East_a)_b

(ROR)_f
> (ROR)_b

△H = (E_a)_f
– (Eastward_a)_b

△H = -ve value

(Due east_a)_f
= △H Only one can be possible for Exothermic Reaction

(E_a)_f
> △H

(E_a)_f
< △H

Read More than:Exothermic Reaction

Endothermic Reaction

(E_a)_f
> (Due east_a)_b

(ROR)_f
< (ROR)_b

△H = (E_a)_b
– (East_a)_f

△H = +ve value

(E_a)_f
> △H (Ever )…………universal

Read More:Endothermic Reaction

Catalysts

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.

Negative Catalysts (Inhibitors)

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

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.

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.

Activation Free energy Formula

The formula used to observe the value of Activation Free energy, East_a
is;

K = Ae^{-Due east}
_a
^/RT

Where

One thousand = Rate Abiding

A = Arrhenius Constant

E_a
= 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
_a
^/RT

Taking log on both sides

ln One thousand = ln A – (E_a

/RT)ln eastward

2.303 log K = two.303 log A – E_a/RT

log Grand = log A – Due east_a
/2.303RT

Solved Examples Related To Activation Energy

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

Solution:

Given grand_ii
= 8× 10
^-2, k_one
= iii × 10^-2, T_one=310K,T₂

=330K

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

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

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

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

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

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

E
_a

= 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
^-ii
 to 5×10
^-ii

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

Solution:

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

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

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

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

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

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

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

East
_a

= 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
^-ii
at 0C and 30
C. Calculate the activation free energy of the reaction?

Solution:

Given g
₂

= 6 × ten
^-2
, thousand
₁

= 2 × ten
^-ii
, T
₁
= 273K, T
₂

= 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
_a

= 25,188.74 J/mole

= 25.188 kJ/mol