Gas laws in chemistry

len Alfred Ajibola - 16th February, 2023 @ 03:06 PM

Topics in Chemistry

Gas laws in chemistry Charles's law explained Calculation questions on Charles's law Examples of Charles's law in real life Boyle's law explained Calculation questions on Boyle's law Examples of Boyle's law in real life Summary on the kinetic molecular theory of gases Postulates of kinetic theory of gases Avogadro's number explained with worked examples Mole and Avogadro's Number explained Le Chatelier's Principle: Changes in concentration and pressure 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 What are mixtures? Characteristics of mixtures

Academic Questions in Chemistry

Please click here to see all Questions and Answers

With regards to redox reactions, which of the following statement is wrong?

  • A. Redox reaction are examples of chemical change

  • B. Reduction is the gain of electron

  • C. Substances that donates election during chemical reaction are termed reductants

  • D. Oxidizing agents are always reduced in chemical reactions

  • E. Oxidation occurs at the cathode in electrolysis

  • F. Hydrogen is a reducing agent

In chemistry, physical change is associated only with the rearrangement of molecules while the internal composition of the substance remains the same.

  • A. True

  • B. False

_____ electron(s) is a term that describes the number of electron(s) in the outermost shell of an atom.

  • A. Outer

  • B. Excess

  • C. Valence

  • D. Positive

  • E. Negative

  • F. Last

_____ is the negative electrode in electrolysis.

  • A. Anode

  • B. Anion

  • C. Cathode

  • D. Cation

  • E. Ion

  • F. Electrolyte

Electrovalent Bond - Len Academy

The above diagram shows the _____ type of bond.

  • A. Covalent

  • B. Polar covalent

  • C. Coordinate covalent

  • D. Metallic

  • E. Van dear walls

  • F. Ionic

 Metals are referred to as _____ in their impure state.

  • A. Diluted

  • B. Consecrated

  • C. Coloured

  • D. Ores

  • E. Stained

  • F. Strained

Metals generally have the quality to shine, glow, sparkle, glitter, reflect light and be polished. This characteristic of metals is termed _____.

  • A. State

  • B. Ductility

  • C. Luster

  • D. Malleability

  • E. Hardness

  • F. Inflorescence

The _____ spectrometry experiment conducted on isotopic elements gave a confirmation for the existence of isotopes.

  • A. Mole

  • B. Volume

  • C. Weight

  • D. Number of moles

  • E. Mass

  • F. Amount of substance

Gas Laws:

Gases are considered as one of the states of matter. They generally show similar behaviour when certain conditions like pressure, temperature, volume, mass and amount of substance (mole) are equal. However, a slight change in one of these conditions will result into a deviation. These deviations are analyzed and calculated through the gas laws.

Please read on gases and their characteristics here.


The gas laws were created around the 18th century by some notable scientists. As stated earlier, these laws basically describe the behaviour of gases at varying conditions like temperature, pressure and volume. The laws are named after the scientists who discovered them. They include the following:


1. Boyle's Law: This law was described by an English scientist named Robert Boyle in 1662. He worked on the relationship between the pressure and volume of a gas.

Boyle's law states that the volume of a gas is inversely proportional to its pressure provided the temperature remains constant.

This law is also referred to as Mariotte's law.

  • PV = k

  • P = Pressure

  • V = Volume

  • k = Constant 

Please read the detailed explanation on Boyle's law here.


2. Charles's Law: This law is sometimes referred to the law of volumes. It was formulated by a French physicist named Jacques Charles in 1780. He worked on the relationship between the volume occupied by a gas and its absolute temperature.

Charles's law state that the volume of a given mass of a gas is directly proportional to its absolute temperature, provided the pressure remains constant.

  • V = T

  • V/T = k

  • V = volume

  • T = Temperature

  • k = Constant

Please read the detailed explanation on Charles's law here.


3. Avogadro's Law: This law (or hypothesis) is named after Amedeo Avogadro (August 9, 1776 - July 9, 1856), an Italian mathematical physicist. He formulated his hypothesis in 1812. He worked on the relationship between the volume occupied by a gas and the amount of gaseous substance.

Avogadro's law states that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules.

  • V = n

  • V/n = k

  • V = Volume of gas

  • n = amount of substance for the gas (measured in moles)

  • k = Constant

This law is also termed as Avogadro's hypothesis, Avogadro-Ampère's hypothesis or Avogadro's principle.

Please read more on the mole concept and Avogadro's number here.


4. Gay Lussac's Law: This law is sometimes referred to as the law of combining volumes of gas; and was put forward by a French scientist, Joseph-Louis Gay-Lussac's law in 1808.

Gay Lussac's law of combining volumes states that, when gases undergo chemical reaction, they do so in simple whole number ratios to one another, provided that the temperature and pressure of the reacting gases and their products remain constant.

According to the law of combining volumes, the ratio between the volumes of gaseous reactant and products are expressed in simple whole numbers.

Please read on emperical formula here.


Meanwhile, understand that Gay-Lussac's law also shows a relationship between the pressure and temperature of a gas at constant volume. It states thus:

  • At a constant mass and volume, the pressure of a gas is directly proportional to the temperature. Therefore, as temperature increases, the pressure will also increase and vice versa. This law may sometimes be referred to as Amonton’s law.

The proportionate increase in pressure and temperature results from the collision of gas molecules with one another and the walls of the container.

Please read the postulates of kinetic theory of gases here.

  • P = T

  • P/T = k

  • P = Pressure exerted by the gas

  • T = Absolute temperature of the gas

  • k = Constant.


5. Dalton's Law of Partial Pressures: This law may simply be referred to as Dalton's law, and it is applicable to ideal gases. It is an empirical law put forward by John Dalton, an English chemist, in 1801. This law determines the individual pressures of each gas in a mixture of gases. By mixture of gases, we mean that the gases are only physically combined, and not chemically combined.

Please read on mixtures and their characteristics here.

Dalton's law of partial pressures states that the total pressure of gases exerted in a mixture of non-reacting gases is equal to the sum of the partial pressures of each of the component gases.

The pressure exerted by each gas is termed partial pressure.

  • PTotal = PGas 1 + PGas 2 + PGas 3 + ... PGas n

  • Where PTotal = Total pressure of the gaseous mixture.

  • PGas = Partial pressure of each gas

You can read on changes in temperature and pressure in dynamic equilibrium here.


If the total pressure is known and the moles of each component gas are known, the partial pressure can be calculated using the formula:

  • Px = PTotal (nx / nTotal)

  • Px = Partial pressure of gas x

  • PTotal = Total pressure of all gases

  • nx = Number of moles of gas x

  • nTotal = Number of moles of all gases


If the total gas is collected over water, then it may become saturated with water vapour. In this instance, the total pressure becomes:

  • PTotal = PGas + PWater vapour

You can read on physical and chemical change in chemistry here.


General Gas Equation

The gas laws; that is: Boyle's law, Charles's law, Avogadro's law, Gay Lussac's law and Dalton's law of partial pressures have opened up our understanding on the relationship between the temperature, pressure, volume and amount of a sample of gas. Together, these gas laws are combined into a general gas equation or the ideal gas law.

The ideal gas law states that the volume of a given amount of a gas is directly proportional to the number of moles of the gas, directly proportional to its kelvin temperature and inversely proportional to the pressure.

pV = nRT

This law was first stated by Benoît Paul Émile Clapeyron in 1834.

Please read worked examples on Boyle's law here.


In order to derive the general gas equation (pV = nRT), three laws were conbined. These are: Boyle’s law, Charles’s law and Avogadro’s law respectively. This is summarized below:

  • Boyle’s law V ∝ 1/P (where T and n are constant)

  • Charles’s law V ∝ T (where P and n are constant)

  • Avogadro’s law V ∝ n (where P and T are constant)

  • V = Volume, P = Pressure, T = Temperature and n = Amount of gas in moles.

Please read calculation questions on Charles's law here.


If we combine these laws, we will have:

V ∝ nT/P

pV= nRT

Where R is a proportionality constant

This is the ideal gas equation. This equation is applied in solving problems with a change in any of these four variables, that is: n, P, V and T.

You can read on molecular mass here.


It is noteworthy to state that the ideal gas law summarizes the behavior of gases under various conditions; an can be used to solve problems regarding a change in the n, P, V and T variables. However, it still has its limitations.

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Amazing facts in Chemistry

Plastic and Glass can decompose, but not in our lifetimes. It takes an average time of 450 years for plastics to decompose. As for the decomposition of glasses, it takes about 4,000 years

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.

Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools

Water 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

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

Below are the physical properties of metals:

  1. They exist in solid state.

  2. The have high densities.

  3. They are good conductors of heat and electricity.

  4. The have the ability to be polished, to glow, sparkle and reflect light.

  5. They can be bent, flattened and made into sheets called foils.

  6. They can be drawn into wires.

  7. Iron undergoes magnetism while most metals are poorly magnetized.

  8. They typical have high melting point.

  9. They generally have high boiling point.

  10. With the exception of lithium, sodium and potassium, most metals are generally hard.

  11. They have the ability to make sound when in contact with other objects or metals.

  12. Please read details on the physical properties of metals here

John Dalton is an English chemist who brought clarity into the composition of matter and the basis for their chemical reactions.

Below are Dalton's Atomic Theory:

  1. All matter consists of tiny indivisible particles called atoms.

  2. Atoms of the same element are identical to each other in every aspect because they have the same shape and mass, while atoms of different elements are different in all respect.

  3. Atoms are indestructible and can neither be created nor destroyed.

  4. Atoms of different elements can combine with each other in simple whole number ratios to form compounds.

  5. Atoms of the same element share similar physical and chemical properties. They can also combine in more than one ratio to form two or more compounds.

Meanwhile, understand that the above theories of John Dalton had been modified.

Please read on Dalton's atomic theory and its modifications here

Periodic Table - Len Academy

The periodic table, also called periodic table of elements or Mendeleev's table, is a table that shows an organized arrangement of the 118 chemical elements according to their atomic number.

Out of the 118 elements; elements 1 - 94 are present in nature while elements 95 - 118 are synthesized artificially.

The manner at which elements are arranged on this table reveals some similarities in their electronic configurations and chemical properties.

Please read on the periodic table of elements here.

A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)

  • Solution:

Step 1: Identify the given parameter from the question.

  • Fe = 69.94%,   O = 30.06%.

  • Empirical formula = Fe?O?


Step 2: Convert the percentages to gram. (just attribute grams to the %).

  • 69.94% = 69.94g while 30.06% = 30.06g


Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in emperical formula.

  • Mole of Fe: 69.94/55.85 = 1.252mol

  • Mole of O: 30.06/16 = 1.879mol


Step 4: Divide both sides by the smallest mole ratio.

  • Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1,    1.879/1.252 = 1.5

  • We now have the formula = Fe1O1.5


Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number '2' is the smallest whole number that will make '1.5' and '1' whole numbers when multiplied by it.

  • For iron (Fe), we will have 1 x 2 = 2

  • For oxygen (O), we will have 1.5 x 2 = 3


Step 6: Write the empirical formula.

  • The empirical formula= Fe2O3

  • Iron(III)tetraoxosulphate(VI)

In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.

Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:

  1. Alkanes

  2. Alkenes

  3. Alkynes

They are shown in the image below:

Alkanes, Alkenes and Alkynes - Len Academy

It's important to note the followings:

  • Alkanes have single bonds (only) in their structures.

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

  • Alkynes always have a carbon-carbon triple bond present in their structure.


Aromatic hydrocarbons are classified into:

  • Arenes: They contain benzene ring as a structural unit. Below is the structure of a benzene ring.

Benzene Ring - Len Academy


  • Nonbenzenoid aromatic hydrocarbons: They possess special stability but lack a benzene ring as a structural unit.