Question

Q02 Why fugacity is called effective pressure? What is difference between given pressure and effective pressure

Answer 1

Solution: The term fugacity is widely used in solution thermodynamics to represent the behaviour of real gases. In case of idea gas we assume that the gas molecules as point mass and there is no interaction between the molecules. But in case of real gases there is interaction forces( attraction or repulsion) between the molecules. So the pressure exerted by a real gas is not same as in the case of idea gas where there is no interaction between the molecules. Therefore the fugacity is called effective pressure in case of real gases.

Mathematically, fugacity is proportional to pressure and in case of ideal gas it is equal to pressure as the proportionality constant becomes 1. The definition of fugacity is compleated by stating that.

Lim (f/P) =1

p-->0  

Differences

1. Fugacity has interaction forces to conut which pressure does not have to.

2. Fugacity is proportional to pressure and equal in case of ideal gas.

3. Fugacity is only calculated for real gas.