Fugacity

Ankita Nama semester 1

1. A PRESENTATION ON CONCEPT OF FUGACITY S.P.C. GOVT. COLLEGE , AJMER Presented by - Ankita nama M.Sc. Chemistry SEMESTER- 1 ST 2022

2. CONTENTS Introduction Concepts of Fugacity Reference

3. INTRODUCTION The concept of Fugacity was introduce by Gilbert newton Lewis. Fugacity is derived from Latin word fleetness or the Escaping Tendency. Fugacity is widely used in solution thermodynamic to represent the behaviour of real gases.

4. Concepts of fugacity The concept of fugacity to represent the actual behaviour of real gases. for an infinitesimal reversible change occuring in a system , we have from dG = VdP - SdT dT =0 so, dG = VdP …..(1)

5. let the system be under isothermal condition , For 1mole of an ideal gas, PV= RT V = RT/P So, from eq.(1), We have, dG = RT( dP /P) dG = RTd (ln P) …….(2)

6. For a real gas, a function f known as fugacity is introduced and is defined in such a manner that the realation , dG = RTd log f .........(3) always hold good , whether the gas is ideal or real. On integration of eq.(3) we get, G = RTd log f + c .........(4)

7. Where , c = integration constant which is dependent on the temprature and nature of the gas. On integrating equation (3) between proper limits , we get , ………(5)  

8. Where , the subscripts 1 and 2 represent the initial and final states , respectively. for an ideal gas , eq.(5) becomes , ………(6) comparing eq. (5) and(6) , we see that , Fugacity if we take proportionality constant as unity , then Fugacity = Pressure  

9. For a real gas , the values of f and p are not proportional to one another and f/p is not constant. As the pressure is lowered, the behaviour approaches that of ideal behaviour . So, the gas at very low pressure is taken to be the refrence state and it is postulated that: = 1  

10. this postulate makes the evalution of actual fugacities at various pressure possible. S ince pressure is expressed in atmosphere; fugacities are also expressed in atmosphere.

11. reference Authors:- Dr. J.N. Gurtu , A. Gurtu Book:- Pragati’s Advanced physical chemistry