Gas Law

GAS LAWS

Boyle’s law

• At constant temperature, the pressure of a fixed amount (i.e., number of moles n) of gas varies inversely with its volume. This is known as Boyle’s law.

• If a fixed amount of gas at constant temperature T occupying volume V₁ at pressure p₁ undergoes expansion, so that volume becomes V₂ and pressure becomes p₂, then according to Boyle’s law :

• Experiments of Boyle, in a quantitative manner prove that gases are highly compressible.
• Also , With the help of Boyle’s Law , we determine that

• This shows that at a constant temperature, pressure is directly proportional to the density of a fixed mass of the gas.

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Charles law

• Charles’ law, states that pressure remaining constant, the volume of a fixed mass of a gas is directly proportional to its absolute temperature.

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• Charles found that for all gases, at any given pressure, graph of volume vs temperature (in Celsius) is a straight line and on extending to zero volume, each line intercepts the temperature axis at – 273.15 ° C.
• Slopes of lines obtained at different pressure are different but at zero volume all the lines meet the temperature axis at – 273.15 ° C

Absolute Zero –

• The lowest hypothetical or imaginary temperature at which gases are supposed to occupy zero volume is called Absolute zero.

Gay Lussac’s Law

• It states that at constant volume, pressure of a fixed amount of a gas varies directly with the temperature.

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Avogadro’s law

• It states that equal volumes of all gases under the same conditions of temperature and pressure contain equal number of molecules.
• If the amount of gas increases, then so does its volume.
• 
• V = k₄n
• The number of molecules in one mole of a gas has been determined to be 6.022 X 10²³ and is known as Avogadro constant.

Standard temperature and pressure (STP)

• Standard temperature and pressure means 273.15 K (0°C) temperature and 1 bar (i.e., exactly 10⁵ Pascal) pressure.
• Volume of 1 mole of any gas at STP is 22.4 L

Graham’s Law

• According to this law, the rate of diffusion of a gas is inversely proportional to the square root of its density.
• 
• 

Since molecular weight of gas is equal to twice the vapor density

• 
• Using equation 2 in equation 1 , we get
• 
• Hence, Graham’s Law of diffusion can also be stated as the rate of diffusion of gases is inversely proportional to the square root of their molecular masses.