States of Matter – Notes (Topic 1)

The three states of matter are solid, liquid, and gas.
Represented by a simple model where particles are shown as small solid spheres.
Gas:
- Particles have the most energy.
- Particles are the most spread apart with a random arrangement.
Liquid:
- Particles have more energy than in a solid, but less than in a gas.
- Particles are closer together than in a gas but have a random arrangement.
Solid:
- Particles have the least energy—they are not moving or only vibrating.
- Particles are arranged regularly and are very closely packed.
Core idea: states of matter differ in particle energy, movement, and arrangement, explained by the kinetic theory.

Interconversions are physical changes (not chemical changes) because they involve forces between particles.
Melting and freezing occur at the melting point:
- solid → liquid: melting
- liquid → solid: freezing
Boiling and condensing occur at the boiling point:
- liquid → gas: boiling
- gas → liquid: condensing
When changing from solid to liquid to gas:
- Particles gain more kinetic energy, move around more, become more randomly arranged, and spread further apart.
When changing from gas to liquid to solid:
- Particles lose kinetic energy, move less, become more regularly arranged, and come closer together.
Significance: these changes are reversible and driven by energy transfer (heat). They illustrate the kinetic theory and phase behaviour.

Diffusion: movement of particles from an area of high concentration to an area of low concentration.
For diffusion to occur, particles must be able to move; therefore:
- Diffusion does not occur in solids (particles can only vibrate, not move from place to place).
Dilution of coloured solutions:
- Coloured solute particles diffuse to areas of lower concentration by moving into the solvent (e.g., water), diluting the colour.
- Practical implication: adding solvent reduces the concentration of a solute.

Solvent: the liquid in which a solute dissolves.
Solute: the substance that dissolves in a solvent to form a solution.
Solution: a homogeneous mixture formed when a solute has dissolved in a solvent.
Saturated solution: a solution in which no more solute can be dissolved in the solvent under the given conditions.

Solubility is defined as the amount of solute that can dissolve in a given amount of solvent under specified conditions.

Symbolically: $ext{solubility} = ext{grams of solute that dissolve in } 100 ext{ g solvent}$
- Practical relevance: guides how much solute can be dissolved at a given temperature (and, for gases, at a given pressure).

General trends:
- Solubility of solids typically increases with temperature. Higher temperature often allows more solid solute to dissolve.
- Solubility of gases typically increases with pressure. Higher pressure can push more gas into solution.
Interpreting a solubility curve:
- Any mass below the curve at a specific temperature indicates an unsaturated solution.
- Any mass above the curve at a specific temperature indicates a supersaturated solution, which is unstable.
Practical use: plotting solubility curves helps predict how much solute will dissolve at a given temperature or how pressure affects gas solubility.

This is a chemistry practical exercise to determine how much solid dissolves in water at a chosen temperature.
Typical steps (illustrative):
- Prepare a saturated solution at the target temperature.
- Filter or decant to remove undissolved solid.
- Weigh dissolved solute or determine concentration by a suitable method.
- Repeat at different temperatures or with different solids to compare solubility curves.

Links to foundational principles:
- Kinetic theory explains how energy affects particle movement and phase changes.
- Energy input (heat) drives transitions between solid, liquid, and gas.
- Solubility concepts connect to molecular interactions between solute and solvent (intermolecular forces).
Real-world relevance:
- Understanding solubility informs cooking, pharmaceutical formulations, environmental science (dissolved pollutants), and industrial crystallization processes.
Ethical/practical considerations:
- Safe handling of chemicals and accurate measurement are essential in practical solubility experiments.
Note: No chemical changes are involved in the phase transitions described; these are physical changes driven by energy and particle arrangements.