Boyle’s Law - Gas Law | Explanation, Graphical verification and Significance | Chemistry Grade XI

Gas Law

Boyle’s Law - Gas Law | Explanation, Graphical verification and Significance | Chemistry Grade XI

Boyle’s Law - Gas Law | Explanation, Graphical verification and Significance

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 P1 and volume V1 of the gas is changed to pressure P2 and volume V2 at constant temperature.
Applying boyles law,
P1V1= k ---------- (ii)
P2V2 = k ---------- (iii)
 
Combining equation (ii) and (iii)
P1V1 = P2V2 
 
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.Volume plotted against pressure

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

Volume plotted against reciprocal of pressureiii. When the product of pressure and volume is plotted against pressure, we obtain straight line parallel to the pressure axis.

PV against PBoyle'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:

  1. 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.
  2. Boyle’s law shows the relationship between pressure and density at a constant temperature.
  3. 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.
  4. Boyle’s law shows how volume changes with the change in pressure at constant temperature.

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