**Gas law**

The law which shows the relation among various properties of a certain mass of gas (Volume, Pressure, Temperature, no. of moles) is called gas law.

**A. Boyle's law: ( 1662)**

In 1662, Robert Boyle performed various experiments and studied the effect of change of pressure on volume at a constant temperature. He formulated mathematical relation between volume and pressure at a constant temperature on the basis of his observation which is known as Boyle’s law.

Boyle’s law states that at a constant temperature, the volume of a certain mass of gas is inversely proportional to pressure. i.e. V is proportional to 1/P

**Explanation of Boyle’s law:**

According to Boyle’s law,

V is proportional to 1/P

V= k/P [ where k is proportionality constant]

PV = k ---------(i)

Let pressure P

_{1}and volume V_{1}of the gas is changed to pressure P_{2}and volume V_{2}at constant temperature.Applying boyles law,

P

_{1}V_{1}= k ---------- (ii)P

_{2}V_{2}= k ---------- (iii)Combining equation (ii) and (iii)

P

_{1}V_{1}= P_{2}V_{2}**Graphical verification of Boyle's law:**

Boyle's law can be verified by plotting various values of volume under different pressure.

**i. When values of volume are plotted against the values of pressure in accordance with the equation volume is plotted against reciprocal of pressure, we obtain a hyperbolic curve.**

**ii. When volume is plotted against the reciprocal of pressure, we obtain a straight line.**

**iii. When the product of pressure and volume is plotted against pressure, we obtain straight line parallel to the pressure axis.**

**Boyle's law in terms of density**

Mathematically,

Boyle's law is: V= K÷P ---------- (i)

We know that

Density(d) = Mass( m)÷Volume(V)

V=m÷d ---------- (ii)

Combining equation (i) and (ii)

m÷d = K÷ P

P= K÷ m× d ---------- (iii)

‘K’ is proportionality constant and ‘m ‘mass of gas taken is also constant.

So removing constant term from equation (iii), we get P directly proportional to d ---------- (iv)

According to boyle’s law at constant temperature, pressure of certain mass of gas is directly proportional to its density.

**Significance of Boyle’s law:**

- Boyle’s law mathematically proves that a certain mass of gas is compressible. Greater the compressibility, the greater will be the density. As a result, pressure increases.
- Boyle’s law shows the relationship between pressure and density at a constant temperature.
- At high altitude, the pressure of gas(air) is less. So, the availability of oxygen is less at high altitude. Because of this, mountaineers take oxygen cylinders with them.
- Boyle’s law shows how volume changes with the change in pressure at constant temperature.

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