States of Matter & Changes of State
CSEC Physics: Structure of Matter
Essential Understanding: Matter is anything that has mass and occupies space. It exists primarily in three states: Solid, Liquid, and Gas. These states differ in how their particles are arranged, how they move, and how they interact with each other.
Properties of the Three States
Solids
Arrangement: Particles are packed tightly in a regular, fixed lattice structure.
Motion: Particles vibrate in a fixed position. They cannot move past one another.
Properties:
- Fixed shape and volume.
- High density (incompressible).
- Strong forces of attraction.
Liquids
Arrangement: Particles are close together but in a random, disordered arrangement.
Motion: Particles can move slowly and slide past each other (flow).
Properties:
- Fixed volume, but takes the shape of the container.
- Medium density (almost incompressible).
- Weaker forces than solids.
Gases
Arrangement: Particles are very far apart with no regular pattern.
Motion: Particles move very fast in random, straight lines, colliding with each other and walls.
Properties:
- No fixed shape or volume (fills container).
- Low density (easily compressible).
- Negligible forces of attraction.
Interactive Particle Lab
Matter Simulator
Objective: Switch between states to visualize how particle behavior changes. Notice the difference in speed and arrangement.
Observation: Particles are vibrating in fixed positions.
Microscopic View: Brownian Motion
Observe how the large “smoke” particle (red) is pushed around by the constant bombardment of tiny, fast-moving air molecules (blue).
Changes of State (Phase Changes)
Matter can change from one state to another by heating (adding energy) or cooling (removing energy). During these changes, the temperature remains constant while the internal arrangement of the particles changes.
Melting
Process: Solid → Liquid
Energy added breaks bonds between particles. Occurs at the melting point.
Freezing
Process: Liquid → Solid
Energy removed allows bonds to form. Occurs at the freezing point.
Evaporation / Boiling
Process: Liquid → Gas
Evaporation occurs at the surface; boiling occurs throughout the liquid at the boiling point.
Condensation
Process: Gas → Liquid
Occurs when gas cools. Particles lose energy and come closer together.
Sublimation
Process: Solid → Gas
Occurs without passing through the liquid state. High-energy particles escape directly.
Deposition
Process: Gas → Solid
Occurs without passing through the liquid state.
Real-World Application: Refrigeration Cycle
A refrigerator uses changes of state to cool food. A refrigerant circulates through the system to continuously remove heat.
Gas refrigerant is compressed by a pump, significantly increasing its temperature and pressure.
The hot gas passes through condenser coils (on the back of the fridge). It releases heat to the surroundings and condenses into a liquid.
The liquid refrigerant passes through an expansion valve, rapidly expanding and dropping drastically in temperature.
The cold liquid travels through evaporator coils inside the fridge. It absorbs heat from the interior and evaporates back into a gas, completing the cycle.
Density Comparison
Because particles are packed differently in each state, the density varies significantly.
Analysis: Gases have a much lower density because the particles are far apart and there is a lot of empty space between them.
Key Examination Insights
Heating Curves: When drawing or interpreting a heating curve, remember that during phase changes (flat parts of the graph), the temperature is constant even though heat is still being added.
- Sloped Parts: The substance is in one state and temperature is changing (Kinetic Energy).
- Flat Parts: The substance is changing state (Potential Energy). The energy is breaking bonds, not speeding up particles.
CSEC Practice Arena
Test Your Understanding
CSEC Examination Mastery Tip
Exam Questions often ask: “Explain why a gas exerts pressure on the walls of its container.”
Model Answer: Gas particles are in constant, random motion. When they collide with the walls of the container, they exert a force. Since pressure is force per unit area, these numerous collisions result in gas pressure.