Matter can appear as solid, liquid, or gas depending on particle motion and intermolecular forces.
1. Kinetic Theory of Matter
Main ideas:
- Matter is made of particles.
- Particles are always moving.
- Temperature is related to average kinetic energy.
- Intermolecular forces and particle distance determine the state.
2. States of Matter
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Particle distance | Very small | Small-medium | Large |
| Intermolecular force | Strong | Medium | Very weak |
| Shape | Definite | Takes container shape | Fills container |
| Volume | Definite | Definite | Variable |
| Compressibility | Very low | Low | High |
3. Density
Density links mass and volume:
$$
\rho = \frac{m}{V}
$$
Useful rearrangements:
$$
m = \rho V
$$
$$
V = \frac{m}{\rho}
$$
Typical units:
- $\mathrm{kg/m^3}$
- $\mathrm{g/cm^3}$
- $\mathrm{kg/L}$
4. Changes of State
- Melting: solid $\to$ liquid
- Freezing: liquid $\to$ solid
- Vaporization (evaporation/boiling): liquid $\to$ gas
- Condensation: gas $\to$ liquid
- Sublimation: solid $\to$ gas
- Deposition: gas $\to$ solid
During a phase change, temperature stays constant while energy is used to break or form intermolecular interactions.
5. Heating Curve
In a heating curve:
- Rising segments: temperature increases in one state.
- Flat segments: phase change at constant temperature.
Two important temperatures:
- Melting point
- Boiling point
6. Gas Laws (qualitative and quantitative)
Gas behavior depends on pressure $P$, volume $V$, and temperature $T$ (in kelvin).
Boyle law (constant temperature)
$$
P_1V_1 = P_2V_2
$$
Charles law (constant pressure)
$$
\frac{V_1}{T_1} = \frac{V_2}{T_2}
$$
Gay-Lussac law (constant volume)
$$
\frac{P_1}{T_1} = \frac{P_2}{T_2}
$$
Combined gas law
$$
\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}
$$
Remember temperature conversion:
$$
T(\mathrm{K}) = T(^\circ\mathrm{C}) + 273.15
$$
7. Everyday Examples
- A perfume smell spreads because gas particles move and diffuse.
- A pressure cooker increases pressure, raising boiling temperature.
- Clothes dry below boiling point by evaporation from the surface.