Key Points

Matter is defined as any substance that has mass and occupies space. In other words, it has both mass ($m$) and volume ($V$).

All matter is composed of very small particles. These particles are in constant, random motion and have spaces between them.

Matter primarily exists in three states: solid, liquid, and gas. These states differ based on the arrangement, energy, and forces of attraction between their constituent particles.

Solids have a definite shape and a fixed volume. Their particles are tightly packed with strong intermolecular forces, leading to high density and negligible compressibility.

Liquids have a fixed volume but no definite shape, taking the shape of their container. Particles in a liquid can slide past one another, which allows liquids to flow.

Gases have neither a fixed shape nor a fixed volume, expanding to fill any container. Their particles are far apart with very weak intermolecular forces, making them highly compressible.

Diffusion is the spontaneous intermixing of particles of different types of matter. The rate of diffusion is fastest in gases, slower in liquids, and negligible in solids, and it increases with temperature.

To convert a temperature from the Celsius scale to the Kelvin scale, add 273. The formula is $T(\text{K}) = T(^\circ\text{C}) + 273$. Kelvin (K) is the SI unit of temperature.

To convert a temperature from the Kelvin scale to the Celsius scale, subtract 273. The formula is $T(^\circ\text{C}) = T(\text{K}) - 273$.

Latent heat of fusion is the amount of heat energy required to change $1$ kg of a solid into a liquid at its melting point without any rise in temperature. This energy is used to overcome the forces of attraction between particles.

Latent heat of vaporization is the amount of heat energy required to change $1$ kg of a liquid into a gas at its boiling point without any rise in temperature. This is why steam at $100^\circ\text{C}$ causes more severe burns than water at the same temperature.

Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Examples include dry ice (solid $\text{CO}_2$) and camphor.

Evaporation is a surface phenomenon in which a liquid changes into vapor at any temperature below its boiling point. This process causes cooling because the escaping particles absorb energy from the surroundings.

The rate of evaporation increases with an increase in surface area, temperature, and wind speed. The rate decreases with an increase in humidity (the amount of water vapor in the air).

The state of matter can be changed by altering pressure. Applying high pressure and reducing temperature can liquefy gases by forcing their particles closer together.

Density is the mass per unit volume of a substance, given by the formula $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$. Generally, solids are the densest, followed by liquids, and then gases.