📘 Raoult’s Law

 Sure! Here's a simple and complete explanation of Raoult’s Law, perfect for Class 12 Chemistry students (CBSE/RBSE/NCERT):

---

📘 Raoult’s Law

(From NCERT Class 12 Chemistry – Chapter 1: Solutions)

---

💡 What is Raoult’s Law?

Raoult’s Law gives a relationship between the vapour pressure of a component in a solution and its mole fraction in the liquid phase.

📌 Statement of Raoult’s Law:
The partial vapour pressure of each volatile component in a liquid solution is directly proportional to its mole fraction in the solution.

---

🔬 Mathematical Expression:

For a binary solution of two volatile liquids, component 1 and 2:

• Partial pressure of component 1:

$$p_1 = x_1 \cdot p_1^0$$

• Partial pressure of component 2:

$$p_2 = x_2 \cdot p_2^0$$

Where:

• $p_1, p_2$ = partial vapour pressures

• $x_1, x_2$ = mole fractions in the liquid phase

• $p_1^0, p_2^0$ = vapour pressures of pure components

---

🧪 Total Vapour Pressure (Using Dalton’s Law):

$$p_{\text{total}} = p_1 + p_2 = x_1 p_1^0 + x_2 p_2^0$$

Also, since $x_1 + x_2 = 1$, we can write:

$$p_{\text{total}} = p_1^0 + (p_2^0 - p_1^0) \cdot x_2$$

---

📈 Graphical Representation:

• Plot of partial vapour pressure vs mole fraction is a straight line.

• Plot of total vapour pressure vs mole fraction is also linear for ideal solutions.

📌 For ideal solutions: no volume change, no heat change, and intermolecular forces between components are similar.

---

📝 Important Points for Exams:

• Raoult’s Law applies only to ideal solutions (obey the law at all compositions).

• Used to calculate vapour pressures, boiling points, and composition of vapour phase.

• More volatile component has a higher pure vapour pressure.

---

🧠 Example:

Let:

• $p_1^0 = 100$ mm Hg (pure A)

• $p_2^0 = 50$ mm Hg (pure B)

• $x_1 = 0.6, x_2 = 0.4$

Then:

$$p_1 = 0.6 \cdot 100 = 60 \text{ mm Hg} \quad p_2 = 0.4 \cdot 50 = 20 \text{ mm Hg}$$ $$p_{\text{total}} = 60 + 20 = 80 \text{ mm Hg}$$

---

Would you like a visual diagram of Raoult’s Law (Fig 2.3) or a video script explanation for this?