Unit 7: States of Matter

Unit 7: States of Matter (8 Teaching Hours)

7.1 Gaseous State

1. Kinetic Theory of Gas and its Postulates

   • The kinetic theory explains the behavior of gases based on the motion of molecules.
   • Postulates:
     • Gases consist of a large number of tiny particles (molecules) in constant random motion.
     • The volume of gas molecules is negligible compared to the volume of the container.
     • Gas molecules exert no force of attraction or repulsion on each other.
     • Collisions between gas molecules and with the walls of the container are perfectly elastic (no loss of energy).
     • The average kinetic energy of gas molecules is directly proportional to the absolute temperature of the gas.

2. Gas Laws

   • Boyle's Law: At constant temperature, the volume of a gas is inversely proportional to its pressure. $P_1 V_1 = P_2 V_2$
   • Charles' Law: At constant pressure, the volume of a gas is directly proportional to its absolute temperature. $\frac{V_1}{T_1} = \frac{V_2}{T_2}$
   • Avogadro's Law: At constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of gas. $V \propto n$

3. Combined Gas Equation Combines Boyle’s, Charles’, and Avogadro’s laws: $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$

4. Dalton’s Law of Partial Pressure The total pressure of a mixture of gases is equal to the sum of the partial pressures of individual gases. $P_{\text{total}} = P_1 + P_2 + P_3 + \dots$

5. Graham’s Law of Diffusion The rate of diffusion of a gas is inversely proportional to the square root of its molar mass. $\frac{\text{Rate}_1}{\text{Rate}_2} = \sqrt{\frac{M_2}{M_1}}$

6. Ideal Gas and Ideal Gas Equation

   • Ideal Gas: A gas that perfectly follows the gas laws under all conditions.
   • Ideal Gas Equation: $PV = nRT$ where $P$ = pressure, $V$ = volume, $n$ = moles of gas, $R$ = universal gas constant, $T$ = temperature.
   • Universal Gas Constant (R): A constant with a value of 8.314 J/mol·K, significant in determining the relationship between pressure, volume, temperature, and the number of moles.

7. Deviation of Real Gas from Ideality

   • Real gases deviate from ideal behavior at high pressure and low temperature.
   • Van der Waals Equation: Corrects the ideal gas equation for intermolecular forces and molecular volume. $\left(P + \frac{a}{V^2}\right)(V - b) = nRT$ where $a$ accounts for intermolecular attractions and $b$ accounts for the finite size of molecules.

7.2 Liquid State

1. Physical Properties of Liquids

   • Evaporation and Condensation:
     • Evaporation is the process where molecules at the surface of a liquid gain enough energy to become a gas.
     • Condensation is the reverse process where gas molecules lose energy and return to the liquid state.
   • Vapour Pressure: The pressure exerted by a vapor in equilibrium with its liquid at a given temperature.
   • Boiling Point: The temperature at which the vapor pressure of a liquid equals the external pressure, causing the liquid to turn into gas.

2. Surface Tension and Viscosity (Qualitative Idea)

   • Surface Tension: The force that causes the surface of a liquid to contract, making it behave like a stretched elastic sheet. It arises from cohesive forces between molecules.
   • Viscosity: The resistance of a liquid to flow, determined by the intermolecular forces within the liquid.

3. Liquid Crystals and Their Applications

   • Liquid Crystals: A state of matter that has properties between those of conventional liquids and solid crystals. Molecules in liquid crystals have an ordered structure but can flow like a liquid.
   • Applications: Liquid crystals are used in display technologies, such as liquid crystal displays (LCDs), in devices like smartphones, monitors, and TVs.

7.3 Solid State

1. Types of Solids

   • Amorphous Solids:
     • These solids lack a well-defined, ordered structure and do not have a definite melting point.
     • Examples: Glass, rubber, and plastics.
   • Crystalline Solids:
     • These have a regular, repeating pattern of atoms, ions, or molecules, forming a crystal lattice. Crystalline solids have a sharp melting point.
     • Examples: Diamond, salt, quartz.

2. Efflorescent, Deliquescent, and Hygroscopic Solids

   • Efflorescent Solids:
     • Solids that lose water molecules to the atmosphere and become powdery.
     • Example: Washing soda ($\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$).
   • Deliquescent Solids:
     • Solids that absorb moisture from the atmosphere and dissolve in it to form a solution.
     • Example: Calcium chloride ($\text{CaCl}_2$).
   • Hygroscopic Solids:
     • Solids that absorb moisture from the air but do not dissolve in it. They only become wet.
     • Example: Silica gel.

3. Crystallization and Crystal Growth

   • Crystallization: The process of forming solid crystals from a homogeneous solution. It occurs when a solution becomes supersaturated, causing the solute to precipitate in a crystalline form.
   • Crystal Growth: Refers to the addition of atoms or molecules to a crystal's surface, expanding its size. The rate of crystal growth depends on factors like temperature, concentration, and the nature of the solute.

4. Water of Crystallization

   • Water of Crystallization: The fixed number of water molecules that are chemically bound within a crystalline solid. These water molecules are essential for maintaining the crystalline structure.
     • Example: $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ (blue vitriol) contains five water molecules as part of its structure.

5. Introduction to Crystal Lattice and Unit Cell

   • Crystal Lattice: A three-dimensional arrangement of atoms, ions, or molecules in a crystalline solid. It represents the repetitive pattern of particles in the entire crystal.
   • Unit Cell: The smallest repeating unit in a crystal lattice that retains the geometric arrangement and properties of the entire lattice. It is characterized by the length of its edges (a, b, c) and the angles between them ($\alpha, \beta, \gamma$).
     • Types of Unit Cells: Simple cubic, body-centered cubic (BCC), and face-centered cubic (FCC).