Gas law - Charles’ Law and Significance of Charles law

 Charles’ Law (V—T relationship)- 

•       In 1787 J Charles proposed a relationship between volume and temperature. It is called Charles’ Law 

• It states that 

               at constant pressure, the volume of a fixed mass of gas is directly proportional to the Kelvin temperature of absolute temperature. If the absolute temperature is doubled, the volume is doubled. Charles’ Law may be expressed mathematically as 

                 V ∝ T  (at constant P and n) -----------------(1) 

            or V =  k2 T                                             ----------- (2) 

where k2 is a constant. 

or  V/T = k2 

If V1, T1 are the initial volume and temperature of a given mass of gas at constant pressure and V2, T2 be the new values, we can write  

 V1/T1 =   K2  = V2/T2  

In other word  

                         At constant pressure the volume of a given mass of a gas increase or decreases by 1/273 of its volume at 00C, for each one degree rise or fall in temperature. 

Let V0 be ----------> the volume of a given mass of a gas at 00C 

     Vt    ------------------------>is its volume at any temperature t0C 

Then the volume, Vt may be written in term of Charles ‘law (at constant pressure) 

Significance of Charles law

·       It's interesting application is the use of hot air balloons in sports and for Meteorological observations. according to Charles’ law gases expand on heating, the larger volume at higher temperature will have lower mass per unit volume and therefore lower density thus hot air is less than cool air. this causes a hot air balloon to rise by displacing the cool air of the atmosphere

on this theory, hydrogen balloons rise higher because of lower density of hydrogen it was developed as a means of transportation across the Atlantic.

·       However, such airships are not being used because hydrogen is inflammable and that transportation will be risky, therefore, hot air balloons are preferred in place of hydrogen balloon