States of Matter & Gas Laws
Matter exists in three common states — solid, liquid, and gas — determined by the arrangement and energy of particles. Gas behaviour is described by three key laws.
A. Properties of the Three States
Solid vs Liquid vs Gas
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed shape | Takes shape of container | No fixed shape |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Particle arrangement | Closely packed, regular lattice | Loosely packed, irregular | Very far apart, random |
| Particle movement | Vibrate in fixed positions | Slide past each other | Move freely at high speed |
| Compressibility | Not compressible | Slightly compressible | Highly compressible |
| Density | High | Medium | Very low |
| Intermolecular forces | Strongest | Moderate | Weakest (negligible) |
Shape
SolidFixed shape
LiquidTakes shape of container
GasNo fixed shape
Volume
SolidFixed volume
LiquidFixed volume
GasNo fixed volume
Particle arrangement
SolidClosely packed, regular lattice
LiquidLoosely packed, irregular
GasVery far apart, random
Particle movement
SolidVibrate in fixed positions
LiquidSlide past each other
GasMove freely at high speed
Compressibility
SolidNot compressible
LiquidSlightly compressible
GasHighly compressible
Density
SolidHigh
LiquidMedium
GasVery low
Intermolecular forces
SolidStrongest
LiquidModerate
GasWeakest (negligible)
B. Changes of State
All Six Changes of State
| Change | Process Name | Heat |
|---|---|---|
| Solid → Liquid | Melting / Fusion | Heat absorbed (endothermic) |
| Liquid → Solid | Freezing / Solidification | Heat released (exothermic) |
| Liquid → Gas | Evaporation / Vaporisation / Boiling | Heat absorbed (endothermic) |
| Gas → Liquid | Condensation / Liquefaction | Heat released (exothermic) |
| Solid → Gas | Sublimation | Heat absorbed (endothermic) |
| Gas → Solid | Deposition | Heat released (exothermic) |
⚡ MCQ Tip Solid→Gas directly = Sublimation (e.g. dry ice CO₂, iodine, camphor, naphthalene). Endothermic = absorbs heat (melting, evaporating, subliming). Exothermic = releases heat (freezing, condensing, deposition).
C. Gas Laws
Boyle's, Charles's, Gay-Lussac's & Ideal Gas Law
| Law | Statement | Formula | Constant |
|---|---|---|---|
| Boyle's Law | Pressure and volume are inversely proportional at constant temperature | P₁V₁ = P₂V₂ | Temperature (T) |
| Charles's Law | Volume and temperature are directly proportional at constant pressure | V₁/T₁ = V₂/T₂ | Pressure (P) |
| Gay-Lussac's Law | Pressure and temperature are directly proportional at constant volume | P₁/T₁ = P₂/T₂ | Volume (V) |
| Ideal Gas Law | Combines all three gas laws | PV = nRT | R = 8.314 J/mol·K |
Boyle's Law
StatementPressure and volume are inversely proportional at constant temperature
FormulaP₁V₁ = P₂V₂
ConstantTemperature (T)
Charles's Law
StatementVolume and temperature are directly proportional at constant pressure
FormulaV₁/T₁ = V₂/T₂
ConstantPressure (P)
Gay-Lussac's Law
StatementPressure and temperature are directly proportional at constant volume
FormulaP₁/T₁ = P₂/T₂
ConstantVolume (V)
Ideal Gas Law
StatementCombines all three gas laws
FormulaPV = nRT
ConstantR = 8.314 J/mol·K
Ideal Gas Law
PV = nRT
P = pressure (Pa) · V = volume (m³) · n = moles · R = 8.314 J/mol·K · T = temperature (Kelvin)
Temperature Conversion
T (Kelvin) = T (°C) + 273
Gas law calculations MUST use Kelvin — never Celsius directly
⚡ MCQ Tip Boyle's = P×V constant (inverse). Charles's = V/T constant (direct). Gay-Lussac's = P/T constant (direct). PV=nRT combines all. Temperature MUST be in Kelvin for all gas law calculations.
Quick MCQ Revision
| Fact | Answer |
|---|---|
| Boyle's Law | P₁V₁ = P₂V₂ — pressure & volume inversely proportional (constant T) |
| Charles's Law | V₁/T₁ = V₂/T₂ — volume & temperature directly proportional (constant P) |
| Ideal Gas Law | PV = nRT |
| Sublimation | Solid → Gas directly (e.g. dry ice, iodine, camphor) |
| Condensation | Gas → Liquid (exothermic — releases heat) |
| Melting | Solid → Liquid (endothermic — absorbs heat) |
| Gas law temperature unit | Kelvin (K = °C + 273) |
| Most compressible state | Gas — particles far apart, large spaces |
| R value | 8.314 J/mol·K (universal gas constant) |