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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.
The Law of Avogadro
‘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.
Formulas and graphical representations
Avogadro’s law can be represented mathematically using the following formula when pressure and temperature are held constant:
V ∝ n
V/n = k
Where V signifies the volume of the gas, n denotes the amount of gaseous substance present (which is frequently represented in moles), and k denotes a constant value. Increases in the amount of a gaseous substance can be computed by using the following formula: As the amount of a gaseous substance increases, the amount of space taken up by the gas increases proportionally.
V1/n1 = V2/n2 ( = k, as per Avogadro’s law).
In the figure below, you can see a graphical illustration of Avogadro’s law (with the amount of substance on the X-axis and the amount of volume on the Y-axis).
The graph of Avogadro’s Law
It is evident that 0 moles of gas will fill zero volume because the straight line (which implies that two values are directly proportional) goes through the origin.
Derivation
The ideal gas equation, which can be stated as follows, can be used to obtain Avogadro’s law.
PV = nRT
Where,
1.The pressure exerted by the gas on the walls of its container is denoted by the letter ‘P.’.
2.Volume occupied by the gas is denoted by the letter ‘V. “
3.The quantity of gaseous substance is denoted by the letter ‘n’ (number of moles of gas)
4.The universal gas constant is represented by the letter ‘R’.
5.The absolute temperature of the gas is represented by the letter ‘T’.
After rearranging the ideal gas equation, the following equation can be obtained:
V/n = (RT)/P
(RT)/P is a constant in this case (since the temperature and pressure are both constant, as well as the fact that the product/quotient of two or more constants is always a constant). Therefore:
V/n = k
As a result, the proportionality between the volume occupied by a gas and the number of gaseous molecules is established and demonstrated.
Molar Volume of a Gas
According to Avogadro’s law, the relationship between the volume of a gaseous material and the amount of that gaseous substance is a fixed relationship (at constant pressure and temperature). It is possible to calculate the value of this constant (k) with the aid of the equation below:
k = (RT)/P
Examples of Avogadro’s Law
Then it comes to breathing, Avogadro’s law is a perfect illustration. As a result of inhaling, individuals experience an increase in the molar amount of air in their lungs, as well as an increase in the volume of their lungs (expansion of the lungs). An illustration of the volume change caused by an increase in the number of gaseous molecules is shown in the following image.
Another example of Avogadro’s law in action is the deflation of automotive tyres, which is widespread knowledge. It is the release of air trapped inside the tyre that results in a reduction in the number of moles of air contained in the tyre. A decrease in the volume of the gas occupied by the tyre as a result of this causes it to lose its shape and deflate.
Limitations of Avogadro’s Law
Despite the fact that Avogadro’s rule is entirely applicable to ideal gases, it only yields approximate equations for real gases. Low temperature and high pressure both cause real gases to deviate more from ideal behaviour than ideal gases do.
Avogadro’s law is more strictly obeyed by gas molecules with relatively low molecular weights (such as helium and hydrogen) than by heavier molecules, which is an important distinction to make.
CONCLUSION
When equal volumes of different gases are mixed under the same conditions of temperature and pressure, Avogadro’s law states that they will have an equal number of molecules in each volume. This empirical relationship can be easily determined from the kinetic theory of gases under the assumption of an ideal gas by applying the kinetic theory of gases to the situation.
