This document provides an overview of binary liquid systems, including vapor pressure, Raoult's law, ideal and non-ideal solutions, solubility of liquids in liquids, and the lever rule. It discusses how vapor pressure works for solids and liquids and introduces Raoult's law, which states that the vapor pressure of a solution decreases based on the mole fraction of the solute. Ideal solutions obey Raoult's law while real solutions can show positive or negative deviations. Positive deviations occur when interactions between like molecules are stronger, while negative deviations occur when interactions between unlike molecules are stronger. The document also covers the different types of solubility between liquids and uses the lever rule to determine the composition and amount of each phase
2. BINARY LIQUID SYSTEMS
Topics covered
• Vapour pressure, Raoult’s law, Ideal and non ideal solutions,
• Solubility of liquids in liquids-Types
• Lever rule
Prepared by
Dr. Sree Remya T S
Asst Professor
S. N. College ,Kollam
3. VAPOUR PRESSURE
• At any given temperature for a particular solid or liquid, there is a pressure at which the
vapor formed above the substance is in dynamic equilibrium with its liquid or solid form.
This is the vapor pressure of the substance at that temperature.
• At equilibrium, the rate at which the solid or liquid evaporates is equal to the rate that
the gas is condensing back to its original form.
• All solids and liquids have a vapor pressure, and this pressure is constant regardless of
how much of the substance is present.
4.
5. RAOULT’S LAW
• In the 1880s, French chemist François-Marie Raoult discovered that
when a substance is dissolved in a solution, the vapor pressure of the
solution will generally decrease. This observation depends on two
variables:
• the mole fraction of the amount of dissolved solute present and
• the original vapor pressure (pure solvent).
Psolution=χsolventP0
solvent
Raoults law is applicable for dilute solutions only
Ideal solutions obey Raoults law whereas real solutions does not
6. IDEAL SOLUTIONS
• Solutions which obey Raoults law at all concentrations and at all
temperatures.
• If A and B form ideal solution, then in terms of interactions
A-A~ B-B~A-B
Also the solute-solute interaction and solvent-solvent interaction is
almost similar to the solute-solvent interaction.
∆Hmixing =0 and ∆Vmixing =0
Eg: n- hexane and n -heptane
Benzene-toluene
8. Real or Non ideal solutions
• Deviate from Raoults law
• Three types
• Type 1- Show small positive deviations from Raoults law, eg: benzene-
toluene
• Type 2- Show large positive deviations from Raoults law, eg: Water-
propanol, water-ethanol
• Type 3- Show large negative deviations from Raoults law, eg:water-
HNO3, water-H2SO4
9. Positive Deviation from Raoult’s Law
Positive Deviation from Raoult’s Law occurs when the vapour pressure of component is greater than what is expected in
Raoult’s Law.
For Example, consider two components A and B to form non-ideal solutions. Let the vapour pressure, pure vapour pressure
and mole fraction of component A be PA , PA
0 and xA respectively and that of component B be PB , PB
0 and xB respectively.
These liquids will show positive deviation when Raoult’s Law when:
•PA > PA
0 xA and PB > P0
B xB, as the total vapour pressure (PA
0 xA + P0
B xB) is greater than what it should be according to Raoult’s Law.
•The solute-solvent forces of attraction is weaker than solute-solute and solvent-solvent interaction that is, A – B < A – A or B – B
•The enthalpy of mixing is positive that is, Δmix H > 0 because the heat absorbed to form new molecular interaction is less than the heat
released on breaking of original molecular interaction
•The volume of mixing is positive that is, Δmix V > 0 as the volume expands on dissolution of components A and B
10. Negative Deviation from Raoult’s Law
Negative Deviation occurs when the total vapour pressure is less than what it should be according to Raoult’s Law.
Considering the same A and B components to form a non-ideal solution, it will show negative deviation from
Raoult’s Law only when:
•PA < PA
0 xA and PB < P0
B xB as the total vapour pressure (PA
0 xA + P0
B xB) is less than what it should be with respect to Raoult’s Law
•The solute-solvent interaction is stronger than solute-solute and solvent-solvent interaction that is, A – B > A – A or B – B
•The enthalpy of mixing is negative that is, Δmix H < 0 because more heat is released when new molecular interactions are formed
•The volume of mixing is negative that is, Δmix V < 0 as the volume decreases on dissolution of components A and B
11. Limitations of Raoult’s Law
• There are a few limitations to Raoult’s law.
• Raoult’s law is apt for describing ideal solutions. However, ideal solutions are hard to find and they
are rare. Different chemical components have to be chemically identical equally.
• Since many of the liquids that are in the mixture do not have the same uniformity in terms of
attractive forces, these type of solutions tends to deviate away from the law.
• There is either a negative or a positive deviation. The negative deviation occurs when the vapour
pressure is lower than expected from Raoult’s law. An example of negative deviation is a mixture of
chloroform and acetone or a solution of water and hydrochloric acid.
• Alternatively, positive deviation takes place when the cohesion between similar molecules is greater
or that it exceeds adhesion between unlike or dissimilar molecules. Both components of the mixture
can easily escape from the solution. An example of positive deviation includes the mixtures of
benzene and methanol or ethanol and chloroform.
24. The Lever Rule
The composition and amount of material in each phase of a two phase liquid can be determined using the lever rule.
This rule can be explained using the following diagram.
