Engineering Principles Raoult's Law

1. Gas-Liquid Systems:One
Condensable Component
Submitted By:-
Ilika Kaushik
(19PBT004)
M.Tech Biotechnology, 1st Sem,
SoBT, GBU.
Submitted To:-
Krishan Kumar Sir
GBU.

2. INTRODUCTION
Systems containing several components of which only
one is capable of existing as a liquid at the process
conditions are common in industrial process.

3. These are all examples of such processes.
• Evaporation, Drying
and Humidification
Involves transfer of
liquid into the gas phase.
• Condensation and
Dehumidification
Involves transfer of
condensable species from
the gas to the liquid phase.

4. Saturated Phase and Saturated Vapour
Suppose liquid water is introduced in a chamber
containing dry air.
Temperature= 75°C; Pressure= 760 mm of Hg
(constant)
• Gas phase contains no water and water begins to
evaporate.
• The mole fraction and partial pressure of water
increases.

5. BUT
• Eventually, amount of water in the gas phase and the
rate at which water molecules enter the gas phase
phase reaches ZERO.
• Then no change occurs in composition of either
phase. At that moment:-
Gas phase = Saturated/ in Saturated Phase
Water in gas phase = Saturated Vapour

6. Raoult’s Law (Single Condensable Species)
• Fundamental relation.
• Used in the analysis of equilibrated gas-liquid
systems, containing one condensable species.
• If a gas is:-
At Temperature= T, Pressure= P; Contains saturated
vapour whose Mole Fraction= yi (mol vapour/mol total
gas) and if this vapour is the only species that will
condense if the temperature is slightly lowered;
Then,

7. “The partial pressure of the vapour in the gas equals
the pure component vapour pressure pi*(T) at the
system temperature.”
Hence, Raoult’s Law for Single Condensable Species:
pi = yiP= pi*(T)