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Particle Theory and States of Matter (Integrated Sciences Term 3)

The Particle Theory

  • All matter is made of tiny particles that are constantly moving; behaviour depends on the state of matter and the energy they have.

  • Changes in state, diffusion, Brownian Motion, and gas pressure can be explained by how particles gain or lose energy and interact.

States of Matter

  • Particles in solids vibrate in fixed positions; arranged in uniform rows; particles touch each other.

  • Forces of attraction hold solids firmly in place; particles cannot move places, only vibrate.

  • Particles in liquids are not in uniform rows; they touch and can move past each other; forces of attraction are weaker than in solids.

  • Particles in gases are spread out and move freely; they do not touch each other; little or no attraction between them.

  • Energy: more energy -> more movement/vibration of particles.

Using the Particle Theory (Overview of States)

  • Solids: tightly packed, vibrate in fixed positions.

  • Liquids: close together, can move past each other.

  • Gases: far apart, move freely.

  • Energy increases movement; Energy decreases movement (opposite for freezing).

Changes in States of Matter

  • Solid to liquid (melting): Particles gain energy and break free from fixed positions; can move past each other.

  • Liquid to gas (evaporation): Particles gain more energy and spread out.

  • Liquid to solid (freezing): Particles lose energy and become fixed in place.

  • Gas to liquid (condensation): Particles lose energy and come closer together.

  • Example: When a solid is heated, energy is transferred to particles, allowing melting to form a liquid; Evapouration, Freezing, Condensation are the other transitions.

Diffusion

  • Diffusion is the spread of particles from high concentration to low concentration due to random movement.

  • Occurs in liquids and gases; faster in gases than in liquids.

  • Real-world example: tea leaves diffusing into hot water.

  • Factors affecting rate: temperature, concentration, and particle size.

Brownian Motion

  • Random movement of larger particles (e.g., pollen grains) in liquids or gases.

  • Caused by collisions with much smaller, fast-moving particles in the fluid.

  • First observed by Robert Brown in 1827; later explained by particle theory.

Gas Pressure

  • Gas particles are spread out and move freely; in a sealed container they collide with the container walls.

  • The sum of these collisions produces gas pressure, equal on all sides.

  • Increasing pressure by reducing space: same number of particles in a smaller volume leads to more frequent collisions, raising pressure.

  • Increasing pressure by increasing temperature: higher energy -> faster motion -> more collisions, higher pressure.

Integrated Takeaways

  • Matter states differ due to particle energy and attraction.

  • Phase changes require energy transfer in the direction of the change (endothermic or exothermic steps).

  • Diffusion and Brownian Motion are explained by random particle motion and collisions.

  • Gas pressure arises from particle collisions with container walls and depends on volume and temperature.