States of Matter

1. Solids, Liquids, and Gases

Distinguishing Properties

  • Solids: Fixed shape and volume. Incompressible. High density.
  • Liquids: Fixed volume but no fixed shape (take shape of container). Slightly compressible.
  • Gases: No fixed shape or volume. Highly compressible. Low density.

States of Matter

Particle Structure

State Arrangement Separation Motion
Solid Regular lattice Very close Vibrate about fixed positions
Liquid Random/Irregular Close Slide over each other
Gas Random Far apart Rapid and random in all directions

2. Changes of State

Definitions

Changing States

  • Melting: Solid to liquid.
  • Boiling: Liquid to gas (occurs throughout the liquid at a fixed temperature).
  • Evaporation: Liquid to gas (occurs only at the surface, below boiling point).
  • Freezing: Liquid to solid.
  • Condensing: Gas to liquid.
  • Sublimation: Solid directly to gas (or vice versa).

Kinetic Particle Theory

Changes of state occur when energy is supplied or removed:

  • Heating: Particles gain kinetic energy, vibrate more vigorously, and eventually overcome the attractive forces holding them together.
  • Cooling: Particles lose kinetic energy, move slower, and attractive forces pull them closer together into a more ordered structure.

Heating and Cooling Curves

  • Plateaus: During a change of state, the temperature remains constant despite continued heating or cooling.
  • Reason: Energy is used to break (during melting/boiling) or is released when forming (during freezing/condensing) bonds/attractive forces between particles, rather than changing the kinetic energy (temperature).

3. Behavior of Gases

Effects of Temperature and Pressure

  • Temperature: Increasing temperature increases the kinetic energy of particles, leading to more frequent and energetic collisions. If pressure is constant, volume increases.
  • Pressure: Increasing pressure (by reducing volume) forces particles closer together, increasing collision frequency with container walls.

Kinetic Theory Explanation

  • Temperature (at constant pressure): $$\text{Higher Temp} \rightarrow \text{Higher Kinetic Energy} \rightarrow \text{Faster Motion} \rightarrow \text{Greater Volume}$$
  • Pressure: $$\text{Higher Pressure} \rightarrow \text{Reduced Volume} \rightarrow \text{Particles closer together}$$

4. Diffusion

Concept

Diffusion Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.

Kinetic Theory Explanation

Particles are in constant, random motion. They collide and spread out until evenly distributed.

Rate of Diffusion

The rate of diffusion depends on the relative molecular mass ($M_r$) of the particles:

  • Lighter particles (lower $M_r$) diffuse faster.
  • Heavier particles (higher $M_r$) diffuse slower.
  • Example: Ammonia ($\text{NH}_3, M_r \approx 17$) diffuses faster than Hydrogen Chloride ($\text{HCl}, M_r \approx 36.5$).