A Detailed Definition of Avogadro’s Law

A Detailed Definition of Avogadro’s Law
Get to grips with Avogadro’s Law by understanding the in-depth definition. This comprehensive guide provides a detailed overview of what this influential law entails.
Avogadro’s Law is a thermodynamic law that states that the molar volume of a gas at a given temperature and pressure is equal to the molar volume of any other gas at the same temperature and pressure. This concept forms the basis for many scientific applications, from calculations used in chemistry to understanding how gases behave in different environments.

A Definition of the Avogadro’s Law.
The Avogadro’s Law states that equal volumes of gases under the same temperature and pressure contain equal numbers of molecules. Formulated by Italian scientist Amedeo Avogadro in 1811, the law states that if two different gases with the same temperature and pressure are combined, the molar volume (the volume occupied by one mole) is the same for both. This principle holds true regardless of the gas composition or identity.

Exploring the Relationship Between Volume and Amounts of Gas.
Avogadro’s Law states that when the same number of moles is present in two different volumes, the ratio of pressure to volume will remain constant. In other words, if two gases have the same number of molecules, they must also be at the same temperature and pressure in order for their volume to be equal. This relation between amount and volume can also be used to compare the number of moles in two separate samples of a given gas.

Differentiating Between Absolute Zero and Standard Temperature and Pressure (STP).
To understand Avogadro’s Law better, one must differentiate between absolute zero and Standard Temperature and Pressure (STP). Absolute zero is the temperature at which all molecular motion ceases, while STP is a set of conditions standardly used to measure the pressure and volume of a gas. The STP for most gases is defined as 0°C (273.15 Kelvin) and 1 atmosphere of pressure. When applying Avogadro’s Law, it’s important to remember that you will need to keep both the pressure and temperature constant in order for it to hold true.

Application of Avogadro’s Law in Real-World Situations.
Avogadro’s Law is essential in everyday applications such as in medical chemistry and fuel technology. In medical chemistry, laboratories create standard gas mixtures based on the expected change of volume with a given amount of pressure to study reactions. In fuel technology, engineers use Avogadro’s Law when designing enough space for gasses inside an engine cylinder in order to keep up the desired levels of efficiency.

The Limitations of Avogadro’s law in Modern Chemistry Practice.
Avogadro’s Law isn’t applicable in all areas of modern chemistry. For example, if a given reaction experiences different gas temperature levels or changes in the number of particles in a reaction volume causing the pressure levels to vary, the law is no longer valid. In this situation, engineers have to resort to more advanced formulas derived from Ideal Gas Law (IGL) and Van der Waals Equation (VdWE).

Definition of Avogadro’s Law :“the equal volumes of all gases have equal number of moles” under standard conditions of temperature and pressure.

Standard temperature is 273 K or 00 Celsius

Standard Pressure is 100 kPa

Thus 1 mole of each gas at 273 K temperature and 100 kPa pressure,  will have 22.7 dm3.

22.7 dm3 is called molar gas volume.

Numerically Volume V is directly proportional to number of moles.

V ∝ n

V=kn where k is proportionality constant.


1 mole of O2 and 1 mole of CO2 will have 22.7 dm3 volume at 273 K temperature and 100 kPa pressure. 6.02X1023

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