Pressure - Volume Relationship
When temperature remains constant, the volume of a fixed mass of a gas decreases as the pressure increases, and it increases when the pressure decreases. There is an inverse relationship between pressure and volume (Fig.15.3).
If the pressure on one litre volume of a gas at 760 mm of Hg at a constant temperature is doubled to 1520 mm of Hg at a constant temperature, the volume will be reduced to half i.e., 0.5 litres.
On the other hand if the pressure on one litre of a gas, at 760 mm of Hg is reduced to half i.e. 0.5 atm. (380 mm of mercury), temperature remaining constant, the volume will double i.e. it will become 2 litres.
Remember:-
Volume of a gas is the space occupied by the gas i.e., the volume of the container. The unit of volume: 1 litre = 1 dm3= 1000 cm3 or 1000 ml.
Pressure exerted by a gas is the average force exerted due to the bombardment of the particles on the sides of the container per unit area of the container. The unit of pressure: 1 atmosphere = 76 cm or 760 mm of mercury.
Temperature - Volume Relationship
If the pressure is kept constant, volume of a fixed mass of a gas increases with increase of temperature, measured on Kelvin or Absolute scale, and it decreases with the decrease in temperature.
One litre of a gas at 273 K (Kelvin unit) will double in volume to 2 litres, if the temperature is doubled to 546 K at a constant pressure. On the other hand, 1 litre of a gas at 273 K, will decrease to half its volume i.e. 0.5 litres, if the temperature is lowered to 136.5 K i.e. halved, at a constant pressure.
Remember:-
Temperature is an indicator of the total kinetic energy that the molecules possess. With the increase of temperature kinetic energy increases.
The unit of temperature: Temperature is expressed in Celsius (centigrade) and Kelvin scale. Temperature on the Celsius scale is expressed in oC.
Kelvin temperature, K = Celsius temperature + 273oC
For example Human blood temperature 37oC or = 310 K.
