Chemistry Formulas

Avogadro’s Law Formula

What is Avogadro’s Law?

This article deals with Avogadro’s Law Formula. Avogadro’s law is a gas law that tells us that the total number of atoms or molecules of a gaseous substance happens to be directly proportional to the gaseous substance’s volume at constant temperature and pressure. Furthermore, Avogadro’s law is in close relation to the ideal gas equation because it links volume, pressure, temperature, and amount of substance.

Avogadro's Law Formula

This law is named after Amedeo Carlo Avogadro, who was a famous Italian scientist. Furthermore, the suggestion of Avogadro that if two dissimilar ideal gases occupy the same volume at a constant pressure and temperature then they must have an equal number of molecules.

Derivation of Avogadro’s Law Formula

One can express Avogadro’s law by the following mathematical equation:

V = k.n

Here, V refers to the gas volume, n refers to the number of gas moles.

Furthermore, k happens to be a constant. The definition of k is as RT/P, where R refers to a constant which experts call as the constant of gases, T happens to be the temperature in Kelvin and P represents pressure. Therefore, one can rewrite the Avogadro’s expression as the famous expression for the ideal gas law:

PV = Nrt

Avogadro’s Law Implications

Below are the important consequences of Avogadro’s Law being true:

  • The molar volume of all ideal gases at 1 atm pressure and 0°C is 22.4 liters.
  • If the temperature and pressure of a gas are constant, when the amount increases, then the volume increases.
  • If the temperature and pressure of a gas are constant, when the amount decreases, then the volume decreases.
  • One can prove Avogadro’s Law each time one blows up a balloon.

Avogadro’s Law Examples

The process of respiration happens to be a good example of Avogadro’s law. When someone inhales, the increase in the molar quantity of lungs air is accompanied by an increase in the lungs volume. Another good example of Avogadro’s law can be the deflation of automobile tyres. When the air inside the tyre escapes, there is a decrease in the number of moles of air present in the tyre. Consequently, this results in a decrease in the gas’s volume. So, the tyre loses its shape and deflate.

Limitations of Avogadro’s Law

  1. In spite of being perfectly applicable to ideal gases, Avogadro’s law provides only approximate relationships at bests. Furthermore, the deviation of real gases from ideal behavior increases at high pressure and low temperatures.
  2. It is important to understand that gases with molecules that consist of relatively low molecular masses (such as helium and hydrogen) obey Avogadro’s law to a greater extent in comparison to the heavier molecules.

Uses of Avogadro’s Law

Experts make use of the ideal gas law extensively in chemistry for doing basic calculations of the pressure or the quantity of gas that exists in any vessel or recipient. Also, this law has suffered some fits or optimization for correcting the ideal behavior for real behavior. The basic equation remains, but there have been additions of some corrections factors. Consequently, the resulting expression is useful to chemical and process engineers for the purpose of undertaking various industrial calculations.

Solved Example for You

Question: 11 L of Helium gas exists in a particular recipient. Furthermore, the helium number of atoms is 0.965 mol. If one increases the amount of gas to 0.9 mol, what new volume will result if the temperature and pressure are the same?

Answer: P and T are certainly constants. Therefore, P1T1 = P2T2

Furthermore, PT = n R/V

N1 R/V1 = n2 R/V2

So, V2 = n2 V1/n1 = 11L × 0.9mol/0.965mol = 10.259 L.

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