Changes of State and Conservation of Mass

Here's something brilliant about changes of state - they're completely reversible! When ice melts or water boils, you're witnessing physical changes where no new substances form. The water molecules remain exactly the same whether they're solid, liquid, or gas.

The conservation of mass principle means the total mass never changes during state changes. This happens because the actual number of particles stays constant - they just rearrange themselves differently.

Gas particles are the ultimate free spirits of the particle world. They're spread out with massive gaps between them and almost no forces holding them together. This gives gases their signature properties: no fixed volume or shape, low density, and the ability to be compressed.

Quick Tip: Remember that gas particles move randomly at high speed - imagine a room full of bouncing balls that never stop moving!

Liquid, Solid Properties and Particle Energy

Liquid particles strike a balance between freedom and structure. They're in contact with each other but can still move around randomly. This gives liquids their fixed volume but allows them to flow and take the shape of their container.

Solid particles are locked in place by strong forces of attraction. They can only vibrate about their fixed positions, which explains why solids have both fixed volume and fixed shape along with high density.

Kinetic energy is the key to understanding state changes. When you increase temperature, particles gain more kinetic energy and move faster. Add enough energy, and you'll trigger a state change - solid to liquid to gas.

The density formula $ρ = m/v$ helps you calculate how tightly packed particles are in different states. Solids typically have the highest density, whilst gases have the lowest.

Exam Success: Practice using the density formula with different units - it's a common exam question that's easy marks once you've got the hang of it!