Explain the difference between ideal and non-ideal solutions with suitable examples.

📘 Ideal vs Non-Ideal Solutions

🔵 Step 1: Ideal Solution

An ideal solution is a solution that obeys Raoult's law over the entire range of composition and temperature.

P_i = x_iP_i°

In an ideal solution, the intermolecular attractions between A–A, B–B and A–B molecules are nearly equal.

ΔH_mix = 0

ΔV_mix = 0

Examples: Benzene + Toluene, n-Hexane + n-Heptane.

🟠 Step 2: Non-Ideal Solution

A non-ideal solution does not obey Raoult's law over the entire range of composition.

This occurs when the A–B intermolecular attractions are significantly different from A–A and B–B attractions.

Examples: Ethanol + Acetone, Chloroform + Acetone.

🟣 Step 3: Positive Deviation

When A–B attractions are weaker than A–A and B–B attractions, molecules escape more easily into the vapour phase.

Vapour pressure observed > Vapour pressure predicted by Raoult's law

This is called positive deviation.

Example: Ethanol + Acetone.

🔴 Step 4: Negative Deviation

When A–B attractions are stronger than A–A and B–B attractions, molecules escape less easily into the vapour phase.

Vapour pressure observed < Vapour pressure predicted by Raoult's law

This is called negative deviation.

Example: Chloroform + Acetone.

🎬 3D-Style Molecular Animation

Ideal solution: A–B attraction is approximately equal to A–A and B–B.

A B A B A B

📊 Step 5: Main Differences

Property	Ideal Solution	Non-Ideal Solution
Raoult's Law	Obeys completely	Shows deviation
A–B Interaction	Approximately equal to A–A and B–B	Different from A–A and B–B
ΔHmix	Zero	Non-zero
ΔVmix	Zero	Usually non-zero
Examples	Benzene + Toluene	Ethanol + Acetone

✅ Exam Summary

Ideal Solution → Raoult's Law obeyed

Non-Ideal Solution → Positive or Negative deviation

Positive deviation: A–B attraction weaker → higher vapour pressure.

Negative deviation: A–B attraction stronger → lower vapour pressure.