9.3 Combined Gas law

Combined Gas Law

The combined gas law is an expression obtained mathematically combining Boyle’s and Charle’s laws. A change in pressure, temperature or volume that is brought about by changes in the other two variables can be calculated by using this law.

Figure 9.43 Combined Gas law

Ref: common.wikimedia.org/

Mathematically we can write, when amount of gas (n) is constant,

Here is the graphical relationship between pressure, volume and temperature of a gaseous system.

Figure 9.44 Gas Laws Graphical representation

Ref: common.wikimedia.org/

Example:  A balloon contains 222 L of Helium at 25.⁰C and 760 mm of Hg. What is the volume of the balloon  when it reaches to an altitude where the temperature is -40⁰C and the pressure is 540 mm of Hg?

Ans: V2 is unknown.

222* 760/( 25+ 273)= 566.17= V2*540/(-40+ 273) , V2= 244.3 L or 244 L.

The Combined Gas Law – Explained