Avogadro's law

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Avogadro's law (sometimes referred to as Avogadro's hypothesis or Avogadro's principle) is a gas law named after Amedeo Avogadro who, in 1811,^[1] hypothesized that "Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of particles, or molecules." Thus, the number of molecules in a specific volume of gas is independent of the size or mass of the gas molecules.

As an example, equal volumes of molecular hydrogen and nitrogen would contain the same number of molecules, as long as they are at the same temperature and pressure and observe ideal or perfect gas behavior. In practice, for real gases, the law only holds approximately, but the agreement is close enough for the approximation to be useful.

The law can be stated mathematically as:

.

where:

V is the volume of the gas.

n is the amount of substance of the gas.

k is a proportionality constant.

The most significant consequence of Avogadro's law is that the ideal gas constant has the same value for all gases. This means that the constant

where:

p is the pressure of the gas

T is the temperature of the gas

has the same value for all gases, independent of the size or mass of the gas molecules.

One mole of an ideal gas occupies 22.40 litres (dm³) at STP, and occupies 24.45 litres at SATP (Standard Ambient Temperature and Pressure = 298K and 1 atm). This volume is often referred to as the molar volume of an ideal gas. Real gases may deviate from this value.

References

External links

• Avogadro's law at the University of Fribourg
• Avogadro's law at the Royal Society of Chemistry