States of Matter – Study Notes (NEET – Chemistry)
1. Simple Explanation
States of matter are distinct forms in which material objects exist based on the arrangement and motion of their particles.
- Solid – particles are tightly packed in a regular lattice, vibrate about fixed positions.
- Liquid – particles are close but can slide past each other; fluidity.
- Gas – particles are far apart, move freely, fill available space.
- Plasma – highly ionized gas (rarely encountered in everyday life, but important in astrophysics and high‑temperature processes).
The transition from one state to another is called a phase transition (melting, freezing, evaporation, condensation, sublimation, etc.).
2. Key Points
| Concept | What it Means | Why It Matters for NEET |
|---|---|---|
| Kinetic Molecular Theory (KMT) | Explains behaviour of solids, liquids, gases via particle motion. | Provides basis for understanding pressure, viscosity, surface tension. |
| Intermolecular Forces (IMF) | - London dispersion - Dipole–dipole - Hydrogen bonding |
Determines boiling/melting points, solubility, viscosity – all high‑school core topics. |
| Phase Diagram | Graph of P vs T showing coexistence lines (solid‑liquid, liquid‑gas, etc.). | Helps recall critical point, triple point, and phase change conditions. |
| State Equations | Ideal Gas Law: (PV = nRT) Van der Waals equation for real gases |
Required for quantitative problems on gas behaviour. |
| Density and Volume Changes | (ρ = \frac{m}{V}) ; solids have higher (ρ) than liquids; water expands on freezing. | Essential for questions on buoyancy, specific gravity, and phase change calculations. |
| Phase Change Heat | Latent heat of fusion (∆H_f), latent heat of vaporisation (∆H_v) | Needed for energy‑budget problems (heat of fusion/vaporisation). |
| Thermodynamic Laws | First law: (ΔU = Q - W) Second law: entropy increases |
Provides conceptual framework for heat and work during phase changes. |
2.1 Quick Reference: State Properties
| Property | Solid | Liquid | Gas | Plasma |
|---|---|---|---|---|
| Particle spacing | Small | Medium | Large | Very large |
| Movement | Vibrational | Translational + vibrational | Translational (free) | Translational + ionised |
| Shape | Fixed | Takes container shape | Takes container shape | Takes container shape |
| Compressibility | Low | Moderate | High | Very high |
| Typical IMF | Strong (covalent/ionic) | Moderate (dipole, H‑bond) | Weak (London) | None (ionised) |
3. Worked Example
Problem
A 2.00 g sample of pure water is heated from 25 °C to 125 °C at 1 atm pressure. Calculate the total heat supplied, assuming all water remains liquid and the specific heat capacity of water is (4.18 \text{J g}^{-1}\text{K}^{-1}).
Solution
-
Determine temperature change
[ ΔT = 125 °C - 25 °C = 100 °C ] -
Use the formula for sensible heat
[ Q = m,c_{p},ΔT ] where
(m = 2.00 \text{g}),
(c_{p} = 4.18 \text{J g}^{-1}\text{K}^{-1}). -
Plug values
[ Q = 2.00 \text{g} \times 4.18 \text{J g}^{-1}\text{K}^{-1} \times 100 \text{K} ] [ Q = 836 \text{J} ] -
Answer
Total heat supplied = 836 J (to raise the temperature only; no phase change occurs).
Extension (if phase change occurs)
If the water were heated to 100 °C and then vaporised:
-
Heat to reach 100 °C:
(Q_1 = 2.00 × 4.18 × 75 = 627 \text{J}) -
Latent heat of vaporisation for water:
(\Delta H_v = 2260 \text{J g}^{-1}) -
Heat for vaporisation:
(Q_2 = 2.00 × 2260 = 4520 \text{J}) -
Total:
(Q_{\text{total}} = Q_1 + Q_2 = 5147 \text{J})
4. Revision Summary (Bullet‑Point)
- States of matter: solid, liquid, gas, plasma.
- Kinetic Molecular Theory explains particle motion, pressure, and viscosity.
- Intermolecular Forces (London, dipole‑dipole, hydrogen bonding) dictate phase behaviour.
- Phase diagram shows coexistence lines; remember triple point and critical point.
- Ideal Gas Law (PV = nRT) – use for quick calculations; remember units.
- Real gas behaviour: Van der Waals equation for non‑ideal gases.
- Latent heats: ∆H_f (fusion), ∆H_v (vaporisation).
- Density: (ρ = \frac{m}{V}). Water expands on freezing (ρ ice < ρ water).
- Heat capacity: (q = m c ΔT).
- Thermodynamics: first law (ΔU = Q - W); second law (entropy).