Chemistry - Solutions | Lecture 3
By Abhishek Sengar
Lecture Chapters
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Theory & Quick Notes
1 Vapor Pressure
Vapor Pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.
Equilibrium Condition
Vapor pressure is measured exactly when:
Rate of Evaporation = Rate of Condensation
Note: The vapor pressure of a liquid at its boiling point is exactly equal to the external atmospheric pressure.
Relates the change in vapor pressure with temperature:
2 Raoult's Law
Raoult's Law states that for a solution of volatile liquids, the partial vapor pressure of each component of the solution is directly proportional to its mole fraction present in solution.
1. For Volatile Solutes
Both solute and solvent create vapor pressure.
pA = p°A × xA
pB = p°B × xB
Ptotal = pA + pB
2. For Non-Volatile Solutes
Only the solvent (A) evaporates. Solute (B) does not.
p°B = 0
Psolution = p°A × xA
Upon addition of a non-volatile solute (like NaCl or Glucose) to a volatile solvent (like Water), the vapor pressure of the solution always decreases compared to the pure solvent.
3 Composition in Vapor Phase
Once vapor is formed above the solution, it has its own mole fraction. We use Dalton's Law of partial pressures to find the mole fraction of a component in the vapor phase (denoted as y).
yA = pA / Ptotal
yB = pB / Ptotal
Remember: yA + yB = 1
Want the Complete Detailed Notes?
Read the full comprehensive article for Chapter 1 on our blog, including detailed theory, solved examples, and deep dives for JEE/NEET.
Lecture 3 Checkpoint
Answer these quick questions to solidify your understanding of Raoult's Law.
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ReplyDeleteThis is excellent. Thank you so much