Chemistry

Le Chatelier's Principle: Changes in Concentration and Pressure explained in Dynamic Equilibrium

len Alfred Ajibola - 09th November, 2020 @ 12:38 PM

Topics in Chemistry

Le Chatelier's Principle: Changes in Concentration and Pressure explained in Dynamic Equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their Differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures Mixtures: Characteristics of Mixtures Physical Properties of Matter explained with Examples Chemical Properties of Matter explained with Examples Differences between Physical and Chemical Change Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid State of Matter: Characteristics of Liquids Gaseous State of Matter: Characteristics of Gases Molar Mass, Worked Examples and Differences with Molecular Mass Elements: Characteristics of Elements Salts and Types of Salt in Chemistry


Academic Questions in Chemistry

Please check out our Test Your Knowledge page to see all Questions and Answers

Which of the following statement is false concerning hydrocarbons?

  • A. Hydrocarbons can be aromatic

  • B. Hydrocarbons are made up of carbon and hydrogen only

  • C. Alkynes are aliphatic hydrocarbons

  • D. Alkenes have a carbon-carbon double bond in their structure

  • E. Benzene ring has a carbon-carbon triple bond in its structure

  • F. Hydrocarbons are the main constituents of petroleum and natural gas

The ability of carbon to form long chain of itself is called _____.

  • A. Carbon chain reaction

  • B. Catenation

  • C. Carbontion

  • D. Carbontion

  • E. Organic chemistry

  • F. Carbon moleculation

Calculate the relative molecular mass of methane. (Carbon = 12.001, H = 1.00794).

  • A. 13.00894 amu

  • B. 11.00206 amu

  • C. 12.00794 amu

  • D. 14.001 amu

  • E. 15.001 amu

  • F. 16.033 amu

Which of he following is not a fact concerning gold?

  • A. 24 karat gold is the purest gold element

  • B. It is the 50th rarest metal amongst all elements found beneath the earth crust

  • C. It is the most malleable and ductile pure metal ever known

  • D. It is the only metal with a golden color

  • E. Gold is non toxic and can be eaten with food

  • F. It's present inside the earth crust in all seven continents

Which of the following is not an example of a chemical change?

  • A. The burning of wood
  • B. The melting of candle wax
  • C. The decomposition of food
  • D. The rotting of leaves
  • E. The lightening of a match stick
  • F. None of the above

Which of the following is not a fraction of crude oil?

  • A. Gasoline
  • B. Naphtha
  • C. Benzene
  • D. Wax
  • E. Paraffin
  • F. Lubrication Oil

The Separating Funnel is a technique used in the separation of mixtures. Another name for Separating Funnel is the _____ Funnel.

  • A. Partition
  • B. Separatory
  • C. Division
  • D. Liquid
  • E. Half
  • F. Dividing

2NH4+(aq) + Ag+(aq) -> 2H4AgN

The equation above represents _____ acid.

  • A. Svante Arrhenius'

  • B. Brønsted–Lowry's

  • C. Gilbert Lewis'

  • D. Avogadro's

  • E. Sir Isaac Newton's

  • F. Albert Einstein's

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Le Chatelier’s Principle:

A system in chemical equilibrium can be controlled or altered in an attempt to favour either the forward or backward reaction; (that is, the equilibrium position). Some of these changes include a change in concentration, pressure and temperature. The dynamics of these changes will be explained in this article.

You can read on the concept of dynamic equilibrium here.

According to French Chemist - Henry Louis Le Chatelier, an altered system (in terms of changing its concentration, pressure and temperature) will adjust itself by shifting equilibrium to the right or left in order to counteract or undo the change. This is the concept of Le Chatelier’s Principle.

Le Chatelier’s Principle state that when a system in dynamic equilibrium is subjected to any change or alteration, the system will adjust itself in order to counteract or revert the applied change.

 

Factors that affect Equilibrium

Below are the explanations of some factors that can change or alter equilibrium:

 

  • A change in concentration

The equation below will be used to explain how a change in concentration affects dynamic equilibrium according to Le Chatelier’s principle:

2SO2(g) + O2(g) ⇌ 2SO3(g)

From the above equation, if the concentration of either or both reactants (2SO2(g) + O2(g)) are increased, the forward reaction will be favoured, thus shifting equilibrium to the right. As a result, more reactants are available for usability and this ultimately favours the forward reaction because more products are formed (and the amount of reactants decreases appropriately).

You can read on the differences between static and dynamic equilibrium here.

Similarly, if the concentration of the product (2SO3(g)) is increased, the backward reaction is favoured as equilibrium shifts towards the formation of reactants. This indirectly increases the amount (or concentration) of the reactants; thus consequently reverting the system into dynamic equilibrium with time.

In summary:

2SO2(g) + O2(g) ⇌ 2SO3(g)

If the concentration of the reactants (2SO2(g) + O2(g)) increases or those of the products (2SO3(g)) decreases then:

  • The formation of more products will be favoured.

  • The added reactants are converted to more SO3.

  • The reaction's equilibrium shift towards the right.

  • Forward reaction is favoured.

 

If the concentration of the reactant decreases or those of the product increases:

  • The formation of more reactants will be favoured.

  • The added products (S03) will be converted to SO2 and O2 respectively.

  • The reaction's equilibrium shift towards the left.

  • Backward reaction is favoured.

Note: In practical terms, if the cost of 2SO3(g) is high while those of the reactants are relatively cheap, then more 2SO3(g) can be economically produced by adding more of the cost friendly reactants to the reaction.

Change in Concentration - Dynamic Equilibrium - Len Academy

Note: A change in the concentration of the reactants or products neither increases or decreases the equilibrium constant. It only shifts the position of equilibrium (either to the right or left). This is because the system counteracts the change by adjusting itself (according to Le Chatelier’s Principle). For this reason, the equilibrium value always remain constant regardless the amount of changes made on the concentration of the reactants, products or both.

You can read on salts in chemistry here.

 

  • A change in pressure

A change in pressure only becomes effective when the reacting system includes at least one gaseous substance. This is true because pressure is effected when gas molecules hit the walls of their container (due to their random motion).

The more gaseous molecules you have inside a container, the higher its pressure. The less gaseous molecules, the lesser the pressure it effects inside its container.

Please read more on gases and their characteristics here.

A change in pressure will only shift the position of equilibrium depending on where the change emanates from; but eventually, the system reverts the change, thus bringing it back to a state of dynamic equilibrium in fulfillment to Le Chatelier’s principle.

Note: Similar to 'change in concentration', a change in pressure does not alter the value of equilibrium constant 

Consider the equation below:

2SO2(g) + O2(g) ⇌ 2SO3(g)

If the pressure of the reactants (2SO2(g) + O2(g)) increases or those of the products (2SO3(g)) decreases, then:

  • The formation of more products will be favoured.

  • The added reactants are converted to SO3.

  • The reactions equilibrium shifts towards the right.

  • Forward reaction is favoured.

 

If the pressure of the reactants decreases or those of the product increases, then:

  • The formation of more reactants will be favoured.

  • The added products (S03) will be converted to SO2 and O2 respectively.

  • The reactions equilibrium shifts towards the left.

  • Backward reaction is favoured.

You can read on physical change and chemical change here.

Note: Increasing the pressure on a gaseous reaction shifts the position of equilibrium towards the side with fewer molecules. Conversely, decreasing the pressure on a gaseous reaction shifts the position of equilibrium towards the side with more molecules.
Change in pressure - Dynamic Equilibrium - Len Academy
The explanations so far on 'changes in concentration and pressure' on equilibrium is quite superficial. Le Chatelier’s principle only gives us a quick summary of the reaction procedure. The ideal explanations on equilibrium shifts (when changes are made on concentration, pressure and temperature) are explained in a mathematical expression via the equilibrium constant 'K'.

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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.


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Amazing facts in Chemistry

The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals.

Please read some interesting facts about gold here

Copper is the only metal that is naturally antibacterial. This is why you would see some children utilize 'copper' water bottles in schools

Water actually freezes faster when it’s warm than when it’s cold

Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy.

Please read on modification of Dalton's atomic theory here.

If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.

Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre


NOTABLE POINTS IN Chemistry

A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.

Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.

The large molecules (above) have no specific chemical formula throughout their volume.

Please read more on Carbohydrates and Sugars here

Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the Modifications of Dalton's Atomic Theory.

Please read on Dalton's Atomic Theory and its Modifications here.

Calculate the Relative Molecular Mass of Methane (CH4). (Carbon=12.001 and H=1.00794)

  • Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen
  • Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.
  • 12.001 + (1.00794 x 4)

Molecular Mass of Methane = 16.033 amu

Please read more on molecular mass here


Calculate the Relative Molecular Mass of Water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)

  • Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen
  • Water contains 2 atoms of Hydrogen and 1 atom of oxygen.
  • (1.00794 x 2) + 15.9994

Molecular Mass of Water = 18.015 Da

Please read on Emperical Formula and its Calculations here

Gold ; Len Academy

Below are some facts about gold

  • It is the only metal that has a gold (golden) color.

  • Gold is present inside the earth crust in all the seven continents.

  • Pure gold is soft and very stretchable (It can even be stretched into threads).

  • The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'.

  • Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables.

  • Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants.

  • The term Gold originated from an ancient English word 'geolu' which means yellow.

  • 24karat gold is the purest gold element.

Please read more interesting facts about gold here

An acid is a substance that produces Hydrogen ions (H+) when dissolved in water (or when in the form of an aqueous solution).

Svante Arrhenius definition of Acid

 

An acid is a substance that donates a proton in a chemical reaction.

Brønsted Thomas Martin Lowry definition of Acid

 

An acid is a substance that accept an electron pair in a chemical reaction.

Gilbert Newton Lewis definition of Acid

 

Finally, Acids can also be also defined as substances that gives out hydronium ion (H3O+) when dissolved in water.

 

In summary, all acids will always contain the positive H+ (cation) and an anionic group in their formula. For instance, the acid HCl (Hydrogen Chloride) contains H+ as cation and Cl- as its anion.

Please read the explanations of the above definitions of acid here