Le Chatelier’s Principles are a set of rules that can be used to predict the effect of a change in temperature, pressure, or concentration on a chemical equilibrium.

Le Chatelier’s Principles, also known as the Equilibrium Law, are used to predict the effect of some changes on a system in chemical equilibrium (such as the change in temperature or pressure). The principle is named after the French chemist Henry Louis Le Chatelier.

Le Chatelier stated that when equilibrium is disturbed, the forward and backward reactions adjust to counteract the changes that have been made to the equilibrium conditions.

Table of Contents

Effect of Change of Reactant or Product Concentration on Equilibrium

Effect of Change of Volume, Pressure, or Inert Gas on Equilibrium

Effect of Change of Temperature on Equilibrium

Effect of Catalyst on Equilibrium

When factors such as concentration, pressure, temperature, and inert gases are altered, the equilibrium will shift in a direction that counteracts the effects of the changes.

Le Chatelier’s principles can be utilized to adjust reversible reactions in order to attain desired results (e.g. higher yield). Here is a link to learn more about reversible reactions.

Le Chatelier’s Principle - Video Lesson

Impact of Concentration Changes on Equilibrium and Product Formation

The concentration of the reactants increases when the forward reaction is favoured. According to Le Chatelier’s principles, this is the only way of achieving equilibrium and increasing product formation. Thus, the equilibrium of the reaction shifts towards the use of reactants, resulting in a decrease in the concentration of the reactants.

The backward reaction is favoured when the concentration of the product increases, causing the equilibrium of the reaction to shift towards the production of reactants. Consequently, the concentration of the reactants will be greater.

Example:

This is an example sentence.

This is an example sentence.

Consider a reaction between oxygen and sulfur dioxide to produce sulfur trioxide.

2SO2(g) + O2(g) $\rightleftharpoons$ 2SO3(g)

If the concentration of the reactant increases, then

The equilibrium will move in the direction of decreasing the concentration of the reactants.

More favorable for the forward reaction.

Some of the SO2 reacts with O2 to form SO3.

The equilibrium of the reaction shifts to the right.

If the concentration of the reactant decreases, then

The equilibrium will move towards a higher concentration of the reactants.

More favored for the backward reaction.

Some of the SO3 would change to SO2 or O2.

The reaction shifts towards the left side of equilibrium.

If the product decreases, then prices will likely go down.

The equilibrium of the reaction shifts to increase the concentration of sulfur trioxide.

The forward reaction rate has increased.

Some of the SO2 reacts with O2 to form SO3.

The equilibrium of the reaction shifts to the right.

If the product increases, then

The equilibrium of the reaction shifts to decrease the concentration of sulfur trioxide.

Decrease in the forward reaction rate.

Some of the SO3 would change to SO2 or O2.

The equilibrium of the reaction shifts towards the left.

Effect of Change in Concentration - Video Lesson

Also Read:

Chemical Equilibrium

Ionic Equilibrium - Degree of Ionization and Dissociation

Equilibrium Constant - Characteristics and Applications

How Changes in Volume, Pressure, or Inert Gas Affect Equilibrium and Product Formation

K_p = K_c (R T)Δn = K_c \left(\frac{p}{v}\right)Δn

Change of volume, pressure or inert gases has no effect on the reactions of liquids and solids. However, they may have an effect on gaseous reactions when the difference in the sum of the number of reactant and product molecules (∆n) is not zero.

When Δn = 0:

No Change in Equilibrium and Product Formation will occur according to Le Chatelier’s principles when the volume, pressure, or inert gas is altered.

When Δn > 0:

An decrease in pressure or increase in volume will decrease the formation of the product. Increase of pressure or decrease of volume shall have the opposite effect of increasing the product formation.

Inert gases do not participate in chemical reactions and only contribute to an increase in volume or pressure.

The addition of inert gas increases the volume at constant pressure, thus resulting in an increase in product formation.

The equilibrium of a reaction remains undisturbed when inert gas is added at constant volume, as the partial pressures and molar concentrations of the substances involved in the reaction remain the same. The reaction quotient will only change if the added gas is a reactant or product involved in the reaction.

PCl3 + PCl2 ⇌ PCl5

In the decomposition of phosphorus pentachloride, Δn = +1.

A decrease in pressure or increase in volume decreases the decomposition of PCl5

At constant pressure, the addition of an inert gas increases the formation of PCl5.

At constant volume, the addition of an inert gas decreases the formation of PCl5.

When ∆n is negative:

According to Le Chatelier’s Principle, an increase in pressure or decrease in volume will result in an increase in the formation of the product.

The addition of inert gas at constant pressure increases the volume and decreases the product formation.

At constant volume, the equilibrium remains undisturbed because the addition of an inert gas does not alter the partial pressures or molar concentrations of the substances involved in the reaction. The reaction quotient will only be affected if the added gas is a reactant or product in the reaction.

2N2 + 6H2 ⇌ 4NH3

The formation of ammonia is accompanied by a decrease in the number of moles (∆n = -2). Increasing the pressure or decreasing the volume increases the formation of ammonia.

At constant pressure, the addition of an inert gas decreases the formation of ammonia.

At constant volume, the addition of inert gas increases the formation of ammonia.

Effect of Change in Volume of Equilibrium Mixture - Video Lesson

![Effect of Change in Volume of Equilibrium Mixture]()

Effect of Addition of Inert Gas - Video Lesson

The Impact of Temperature on Equilibrium and Product Formation

The individual reaction in the equilibrium can be either endothermic or exothermic. Likewise, at equilibrium net energy involved may make the reversible reactions either endothermic or exothermic.

According to Le Chatelier’s Principles,

In exothermic equilibrium, an increase in temperature decreases the product formation and a decrease in temperature increases the product formation.

In endothermic reactions, an increase in temperature leads to an increase in product formation, whereas a decrease in temperature results in a decrease in product formation.

Le Chatelier’s Principle on Change of Temperature

For an exothermic equilibrium, according to the Van’t Hoff equation, ∆H will be negative. An increase in temperature will result in a decrease in K2, while a decrease in temperature will lead to an increase in K2. The opposite is true for an endothermic reaction.

Example:

This is an example sentence.

Answer:

This is an example sentence.

Consider a Reaction

2N₂(g) + 3H₂(g) ⇌ 2NH₃(g); ΔH = -92 kJ

Increase in Temperature

This prefers an endothermic reaction because it requires energy.

An endothermic reaction is a reverse reaction and it is favored.

The yield of the product (NH3) decreases.

Decrease in Temperature

This prefers an exothermic reaction because it releases energy.

An exothermic reaction is a forward reaction which is energetically favoured.

The yield of the product (NH3) has increased.

Effect of Catalyst on Equilibrium and Product Formation

A catalyst is a substance that alters the rate of reactions (increase or decrease) without being consumed in the reaction.

In a reversible reaction, the rate of reaction is the same for both the forward and backward reactions.

The ratio of the reaction rates and the equilibrium constant remain unchanged. According to Le Chatelier’s principles, the presence of a catalyst may affect the rate at which equilibrium is attained, but not the equilibrium concentration.

Frequently Asked Questions (FAQs)

What is the effect of adding inert argon gas to the COBr2 ⇌ CO+ Br2 reaction?

The equilibrium of the reaction will shift to the left as the temperature is decreased. This will result in more reactants and less products, meaning that the reaction will produce less water.

The forward reaction is favored.### If we add hydrogen to the reaction, N2 + 3H2 → 2NH3, the reaction will become more favorable.

In order to achieve equilibrium, the reaction shifts towards the products.— title: “Le Chateliers Principle” link: “/le-chateliers-principle” draft: false

Le Chatelier’s Principles are a set of general rules used to predict the effect of a change in temperature, pressure, or concentration on a chemical equilibrium.

Le Chatelier’s principles, also known as the equilibrium law, are used to predict the effect of certain changes on a system in chemical equilibrium (e.g. changes in temperature or pressure). The principle is named after French chemist Henry Louis Le Chatelier.

Le Chatelier stated that equilibrium will adjust the forward and backward reactions to accommodate changes to the equilibrium conditions.

Table of Contents

• Effect of Change of Reactant or Product Concentration on Equilibrium

Effect of Change of Volume, Pressure, or Inert Gas on Equilibrium

Effect of Change of Temperature on Equilibrium

Effect of Catalyst on Equilibrium

When factors such as concentration, pressure, temperature, and inert gases are altered, the equilibrium will shift in the direction that counteracts the effects of these changes.

Le Chatelier’s principles can be used to control reversible reactions in order to achieve desired results (e.g. increased yield).

Le Chatelier’s Principle - Video Lesson

Impact of Concentration Variations on Equilibrium and Product Formation

The equilibrium of the reaction will shift towards the products when the concentration of the reactants is increased, according to Le Chatelier’s principles. This causes an increase in product formation and a decrease in the concentration of the reactants.

The backward reaction is favoured when the product concentration (or pressure) increases, resulting in a decrease in the product concentration and a shift in the equilibrium of the reaction towards the production of reactants. This will lead to a greater concentration of reactants.

Example:

This is an example sentence.

Answer:

This is an example sentence.

Consider a reaction between oxygen and sulfur dioxide to produce sulfur trioxide.

2SO2(g) + O2(g) $\leftrightharpoons$ 2SO3(g)

If the concentration of the reactant increases, then

The equilibrium will shift towards the decrease in the concentration of the reactants.

More favorable for the forward reaction.

Some of the SO2 reacts with O2 to form SO3.

The equilibrium of the reaction shifts to the right.

If the concentration of the reactant decreases, then

The equilibrium will move towards the side with the higher concentration of reactants.

More favored for the backward reaction.

Some of the SO3 would change to SO2 or O2.

The equilibrium of the reaction shifts to the left.

If the product decreases, then

The equilibrium of the reaction shifts to increase the concentration of sulfur trioxide.

The forward reaction rate has increased.

Some of the SO2 reacts with O2 to form SO3.

The equilibrium of the reaction shifts to the right.

If the product increases, then

The equilibrium of the reaction shifts to decrease the concentration of sulfur trioxide.

Decrease in the forward reaction rate.

Some of the SO3 would change to SO2 or O2.

The equilibrium of the reaction shifts to the left.

Effect of Change in Concentration - Video Lesson

Also Check Out:

Chemical Equilibrium

Ionic Equilibrium - Degree of Ionization and Dissociation

Equilibrium Constant - Characteristics and Applications

How Does a Change in Volume, Pressure, or Inert Gas Affect Equilibrium and Product Formation?

K_p = K_c (R T)Δn = K_c (p/v)Δn

Change of volume, pressure, or inert gases has no effect on the reactions of liquids and solids. However, they may have an effect on gaseous reactions when the difference in the sum of the number of reactant and product molecules (∆n) is not zero.

When Δn = 0:

According to Le Chatelier’s principles, altering the volume, pressure, or introducing an inert gas will have no impact on the equilibrium or product formation.

When ∆n > 0:

An increase in pressure or decrease in volume will decrease the formation of the product. Decrease of pressure or increase of volume shall have the opposite effect of increasing the product formation.

Noble gases do not participate in chemical reactions, and only increase the volume or pressure.

At constant pressure, the addition of an inert gas increases the volume, thus resulting in an increase in product formation.

The equilibrium of a reaction remains undisturbed when an inert gas is added at constant volume, as the partial pressures and molar concentrations of the reactants and/or products remain unchanged. The reaction quotient is only affected when the added gas is one of the reactants or products involved in the reaction.

PCl3 + PCl2 ⇌ PCl5

In the decomposition of phosphorus pentachloride, Δn = +1.

A decrease in pressure or increase in volume decreases the decomposition of PCl5

At constant pressure, the addition of an inert gas increases the formation of PCl5.

At constant volume, the addition of inert gas decreases the formation of PCl5.

When ∆n is negative:

According to Le Chatelier’s Principle, an increase in pressure or decrease in volume will lead to an increase in the formation of the product.

At constant pressure, the addition of inert gas increases the volume, thus decreasing the product formation.

At constant volume, the equilibrium remains undisturbed because the addition of an inert gas does not affect the partial pressures or molar concentrations of the substances in the reaction. The reaction quotient is only altered if the added gas is a reactant or product of the reaction.

2N2 + 6H2 ⇌ 4NH3

The formation of ammonia is indicated by ∆n = -2. An increase in pressure or decrease in volume will result in an increased formation of ammonia.

At constant pressure, the addition of an inert gas decreases the formation of ammonia.

At constant volume, the addition of an inert gas increases the formation of ammonia.

The Impact of Variations in Volume on an Equilibrium Mixture - Video Lesson

Effect of Addition of Inert Gas: Video Lesson

The Impact of Temperature Change on Equilibrium and Product Formation

The individual reaction in the equilibrium can be either endothermic or exothermic. Likewise, at equilibrium the net energy involved may make the reversible reactions either endothermic or exothermic.

According to Le Chatelier’s Principles,

In exothermic equilibrium, an increase in temperature decreases the product formation and a decrease in temperature increases the product formation.

In endothermic reactions, an increase in temperature leads to an increase in product formation, while a decrease in temperature results in a decrease in product formation.

Le Chatelier’s Principle on Change of Temperature

For an exothermic equilibrium, as per the Van’t Hoff equation, ∆H will be negative. An increase in temperature will result in a decrease in K2, while a decrease in temperature will result in an increase in K2. The opposite is true for an endothermic reaction.

Given:

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Response:

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Consider a Reaction

2N₂(g) + 3H₂(g) ⇄ 2NH₃(g) ΔH = -92 kJ

Increase in Temperature

This prefers an endothermic reaction because it requires energy.

An endothermic reaction is a reverse reaction and it is favored.

The yield of the product (NH3) decreases.

Decrease in Temperature

This reaction favors an exothermic reaction because it releases energy.

An exothermic reaction is a forward reaction that is favored.

The yield of the product (NH3) has increased.— title: “Le Chateliers Principle” link: “/le-chateliers-principle” draft: false

Effect of Catalyst on Equilibrium and Product Formation

A catalyst is a substance that changes the rate of reactions (increase or decrease) without quantitatively taking part in the reaction.

In a reversible reaction, the rate of change is equal for both the forward and backward reactions.

According to Le Chatelier’s principles, the presence of a catalyst may accelerate or delay the attainment of equilibrium, however, the ratio of the reaction rates and the equilibrium constant will remain the same.

Frequently Asked Questions (FAQs)

What is the effect of adding inert argon gas to the COBr2 ⇌ CO+ Br2 reaction?

The reaction will still be in equilibrium, however the position of the equilibrium may shift to the left as the temperature is decreased.

The forward reaction is favored.### If hydrogen is added to the reaction, the reaction will shift to the right, increasing the yield of ammonia (NH3).

In order to achieve equilibrium, the reaction shifts towards the products.