Avogadro’s Law

Avogadro’s Law

When applied to gases, Avogadro’s law (also known as Avogadro’s principle or Avogadro’s hypothesis) states that the total number of atoms or molecules in a gas (that is, the amount of gaseous substance) is directly proportional to the total volume occupied by the gas at constant temperature and pressure.

Avogadro’s law is closely related to the ideal gas equation in that it establishes a relationship between temperature, pressure, volume, and the amount of substance present in a given gas under certain conditions.

‘Avogadro’s law’ is named after the Italian scientist Amedeo Carlo Avogadro, who proposed that two dissimilar ideal gases occupying the same volume at a given (constant) temperature and pressure must contain an equal number of molecules. Avogadro’s law is based on the assumption that two dissimilar ideal gases have the same number of molecules.

Formula

Avogadro’s law can be expressed mathematically using the following formula when pressure and temperature are held constant:

V ∝ n

V/n = k,

Where V denotes the volume of the gas, n denotes the amount of gaseous substance present (which is often expressed in moles), and k denotes a constant value. Increases in the amount of a gaseous substance can be calculated by using the following formula: As the amount of a gaseous substance increases, the amount of space taken up by the gas increases proportionally.

Avogadro’s law states that V1/n1 = V2/n2 (i.e., k).

Derivation

In order to derive Avogadro’s law, one must first solve the ideal gas equation, which can be expressed as follows:

PV = nRT is a mathematical formula.

Where,

The pressure exerted by the gas on the walls of its container is denoted by the letter ‘P,’ and the volume occupied by the gas is denoted by the letter ‘V.’

The quantity of gaseous substance is denoted by the letter ‘n.’ (number of moles of gas)

The universal gas constant is denoted by the letter ‘R.’

The absolute temperature of the gas is denoted by the letter ‘T.’

The following equation can be obtained by rearranging the ideal gas equation.

V/n = (RT)/P = (RT)/P

(RT)/P is a constant in this case (because the temperature and pressure are both kept constant, and because the product/quotient of two or more constants is always a constant). Therefore:

V/n = k is a mathematical formula.

It is thus possible to demonstrate that the relationship between the volume occupied by a gas and the number of gaseous molecules is linear.

Gas’s Molar Volume of Gas 

According to Avogadro’s law, the relationship between the volume and the amount of a gaseous substance is constant (at constant pressure and temperature). It is possible to determine the value of this constant (k) with the help of the following equation:

k = (RT)/P is a ratio of two numbers.

Using standard conditions for temperature and pressure, the value of T corresponds to 273.15 degrees Kelvin and the value of P corresponds to 101.325 kilograms per square metre of area. As a result, at STP, one mole of a gas takes up the following amount of space:

8 314 J.mol-1.K-1*(273.15 K)/(101.325 kPa) = 22.4 litres is the volume occupied by one mole of gas.

As a result, at STP, one mole of any gaseous substance takes up 22.4 litres of volume.

Illustrations of Avogadros’s Law

The process of respiration is a fantastic illustration of Avogadro’s law in action. As a result of inhaling, humans experience an increase in the molar quantity of air in their lungs, as well as an increase in the volume of their lungs (expansion of the lungs).

Another example of Avogadro’s law in action is the deflation of automobile tyres, which is quite common. In order for the air trapped inside the tyre to escape, the number of moles of air present in the tyre must be reduced in proportion. In turn, this causes a decrease in the volume of space occupied by the gas, resulting in the tyre losing its shape and deflating.

Limitations of Avogadro’s Law

In spite of the fact that it is perfectly applicable to ideal gases, Avogadro’s law can only provide approximate relationships for real gases. At low temperatures and high pressures, the deviation of real gases from ideal behaviour becomes more pronounced.

Avogadro’s law is more strictly obeyed by gas molecules with relatively low molecular masses (such as helium and hydrogen) than by heavier molecules, which is an important point to remember.

Important Factors to Keep in Mind

• Under similar conditions of temperature and pressure, equal volumes of various gases contain an equal number of molecules in their respective states.
• The Avogadro law is only applicable to gas.
• The importance of Avogadro’s law is that it can be used to determine the amount of gas present and the volume of gas present.
• The deflation of automobile tyres is a good example of the Avogadro law in action.
• Using the equation k = (RT)/P, it is possible to calculate the value of the constant.
• In chemistry, the Avogadro law is more commonly used to measure the pressure or the number of gases present in a vessel.
• This is also utilised by chemical and process engineers for the purpose of performing calculations.
• In contrast to gases with higher molecular masses, gases with molecules with lower molecular masses, such as helium and hydrogen, obey the Avogadro law more consistently.
• The process of respiration is yet another example of Avogadro’s law in action, as shown below.
• As long as the temperature and pressure remain constant or close to it, the amount increases, and the volume increases with it.
• When the temperature and pressure are the same or constant, the amount decreases, and the volume decreases as a result of the amount decreasing.
• The Avogadro law was named after the famous Italian scientist Amedeo Carlo Avogadro, who lived in the 18th century.

CONCLUSION

Avogadro’s law (also known as Avogadro’s principle or Avogadro’s hypothesis) states that the total number of atoms or molecules in a gas (that is, the amount of gaseous substance) is directly proportional to the total volume occupied by the gas at constant temperature and pressure.According to Avogadro’s law, the relationship between the volume and the amount of a gaseous substance is constant (at constant pressure and temperature).In spite of the fact that it is perfectly applicable to ideal gases, Avogadro’s law can only provide approximate relationships for real gases. At low temperatures and high pressures, the deviation of real gases from ideal behaviour becomes more pronounced.The Avogadro law is only applicable to gas.The importance of Avogadro’s law is that it can be used to determine the amount of gas present and the volume of gas present.