Charles’ Law - Practice Questions & MCQ

In order to explain it, let us consider the following plot between volume and temperature. 

It shows that the volume of a definite amount of a gas varies linearly with temperature on Celsius scale. It can be given as:
V_t = a + bt 
Here a and b are constants. 

So according to Charle's law, "At constant pressure, the volume of a given mass of a gas increases or decreases by 1/273 of its volume at 0^oC for every one degree centigrade rise or fall in temperature" that is,

Hence "At constant pressure, the volume of a given mass of a gas is directly proportional to its temperature in Kelvin."

Relation between Density and Temperature

Absolute Scale of Temperature or Absolute Zero
As according to Charle's law, we have: 

 

If the temperature of a gas is lowered upto - 273^oC the volume of the gas becomes zero. This temperature is known as absolute zero and this zero point on the scale is called as Kelvin scale. 

The absolute value of this temperature is - 273^oC. At this temperature, pressure, kinetic energy, and heat content Of the gas is also zero. Absolute zero does not indicate thus zero value of the volume of the gas is the indicator. There is no significance of gas laws at this temperature as the gas phase is not observed here as a gas liquefied or solidified before this temperature. 

When a graph is plotted between the volume of the gas against this temperature at constant pressure, it is called isobar and it is always a straight line.

Plots between V vs T

(i) A straight-line graph is obtained. 

(ii) Slope of lines obtained at different temperatures is different 

(iii) The temperature circled is absolute zero temperature (0 K or -273.15^oC) where is 0 K and all the lines meet. 

Isobars: The curves of volume temperature graphs at different fixed pressures are called isobars. 

All gases obey Charles Law at low pressures and high temperatures.

Physical Significance of Charles' Law: 
Hot air balloon technology is based on Charles Law. On increase in temperature air expands. So, the density of air decreases. The hot air in the balloon is less dense and lighter than the atmospheric air. Therefore the balloons filled with hot air rise up for meteorological observations.