class 11 chemistry state of matter notes || class 11 chemistry unit 2

 

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🧪 Chapter: States of Matter (Class 11 Chemistry)

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🔹 Introduction

• Matter exists in three physical states: Solid, Liquid, and Gas.

• The intermolecular forces and thermal energy determine the physical state of a substance.

• Intermolecular Forces: Attractive forces between molecules. Strongest in solids, weakest in gases.

• Thermal Energy: Energy of a body due to the motion of its particles. It opposes intermolecular forces.

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🔹 Types of Intermolecular Forces

1. Dispersion Forces (London Forces):

   • Weakest forces.

   • Present in all molecules (especially non-polar).

   • Caused by temporary dipoles.

2. Dipole-Dipole Interactions:

   • Between polar molecules.

   • Permanent dipoles attract each other.

3. Hydrogen Bonding:

   • Strongest among van der Waals forces.

   • Occurs when H is bonded to highly electronegative atoms (N, O, F).

   • Responsible for many unique properties of water.

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🔹 Gas Laws

1. Boyle’s Law (at constant T)

• Pressure ∝ 1/Volume or $P \propto \frac{1}{V}$

• $$PV=constantPV = \text{constant}

• Graph: Hyperbola (P vs V), straight line (P vs 1/V)

2. Charles’ Law (at constant P)

• Volume ∝ Temperature (K)

• $$VT=constant\frac{V}{T} = \text{constant}

• Graph: Straight line (V vs T)

3. Gay-Lussac’s Law (at constant V)

• Pressure ∝ Temperature (K)

• $$PT=constant\frac{P}{T} = \text{constant}

4. Avogadro’s Law

• Equal volumes of all gases at the same T and P contain equal number of molecules.

• $V \propto n$ (n = number of moles)

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🔹 Ideal Gas Equation

$$PV = nRT$$

Where:

• $P$ = Pressure (atm)

• $V$ = Volume (L)

• $n$ = Number of moles

• $R$ = Gas constant = 0.0821 L·atm/mol·K

• $T$ = Temperature (K)

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🔹 Gas Constant (R)

Units	Value of R
L·atm·mol⁻¹·K⁻¹	0.0821
J·mol⁻¹·K⁻¹	8.314
cal·mol⁻¹·K⁻¹	1.987

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🔹 Dalton’s Law of Partial Pressure

• Total pressure of a gas mixture = sum of partial pressures.

$$P_{total} = P_1 + P_2 + P_3 + \dots$$

• $P_i = X_i \cdot P_{total}$ (where $X_i$ = mole fraction of gas i)

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🔹 Kinetic Molecular Theory of Gases

Main assumptions:

• Gases consist of particles in constant random motion.

• Volume of particles is negligible.

• No attractive/repulsive forces.

• Collisions are elastic.

• Average kinetic energy ∝ temperature (K).

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🔹 Root Mean Square Speed (r.m.s.)

$$u_{rms} = \sqrt{\frac{3RT}{M}}$$

Where:

• $R$ = 8.314 J/mol·K

• $T$ = Temperature in K

• $M$ = Molar mass in kg/mol

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🔹 Deviation from Ideal Gas

• Real gases deviate at high pressure and low temperature due to intermolecular forces and finite molecular volume.

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🔹 van der Waals Equation (Real Gas Equation)

$$\left(P + \frac{a}{V^2}\right)(V - b) = RT$$

Where:

• $a$ = measure of intermolecular forces

• $b$ = volume occupied by gas molecules

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🔹 Liquefaction of Gases

• Gases can be liquefied by cooling and increasing pressure.

• Critical temperature (Tᶜ): Temperature above which gas cannot be liquefied.

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🔹 Properties of Liquids

• Vapor Pressure: Pressure exerted by vapor in equilibrium with liquid.

• Boiling Point: Temp at which vapor pressure = external pressure.

• Surface Tension: Force acting along the surface to minimize area.

• Viscosity: Resistance to flow.

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🔹 Solid State (Brief Overview)

• Fixed shape and volume.

• Strong intermolecular forces.

• Crystalline and amorphous types.

• Not deeply discussed in this chapter but detailed in the “Solid State” chapter.

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🔹 Important Formulas Summary

1. $PV = nRT$ (Ideal Gas)

2. $u_{rms} = \sqrt{\frac{3RT}{M}}$ (Speed)

3. $P_{total} = P_1 + P_2 + \dots$ (Dalton’s Law)

4. $\left(P + \frac{a}{V^2}\right)(V - b) = RT$ (van der Waals)

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