# 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 V
_{1}at pressure p_{1}undergoes expansion, so that volume becomes V_{2}and pressure becomes p_{2}, 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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*Graphs-*

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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.

*Graph - *

- 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.**

*Graph – *

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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 = k
_{4}n - The number of molecules in one mole of a gas has been determined to be 6.022 X 10
^{23}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 10
^{5}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.