Particle Model and States of Matter

Ever wondered why you can't squash water but you can compress air in a bike pump? It's all about how particles are arranged! Solids and liquids are incompressible because their particles are packed tightly together with no gaps, whilst gases have loads of space between particles.

Density tells you how much matter is crammed into a space using the formula: density = mass ÷ volume. Remember the units: density in kg/m³, mass in kg, and volume in m³.

When substances change state (like ice melting or water boiling), the mass stays exactly the same - you're not losing any particles! These are physical changes, which means you can reverse them and get back to where you started.

Internal energy is the total energy stored by all the particles in a system - think of it as their combined movement and position energy. When you heat something, you're pumping energy into these particles, either making them move faster (raising temperature) or helping them break free from their positions (changing state).

Quick Tip: The formula for temperature changes is ΔE = mcΔθ, where c is specific heat capacity - basically how stubborn a material is about changing temperature!

Latent Heat and Gas Behaviour

Specific heat capacity measures how much energy you need to raise 1kg of a substance by 1°C. Some materials like water are really stubborn and need loads of energy, whilst others heat up quickly.

Here's something brilliant: during changes of state, temperature stays constant even though you're adding energy! This energy is called latent heat and it's busy breaking or forming bonds between particles rather than making them move faster.

Specific latent heat tells you exactly how much energy 1kg of a substance needs to change state without changing temperature. Use the formula: energy = mass × specific latent heat. There are two types: fusion (solid to liquid) and vaporisation (liquid to gas).

Gas particles are like tiny pinballs, constantly bouncing around randomly. Their average kinetic energy determines the gas temperature. When you heat a gas in a fixed container, pressure increases because particles hit the walls harder and more often.

Boyle's Law states that for a fixed amount of gas at constant temperature: pressure × volume = constant. Squash the gas into half the space, and pressure doubles! When you do work on a gas (like using a pump), you increase its internal energy and usually its temperature too.

Remember: Gas pressure comes from billions of tiny particle collisions with container walls - it's like being pelted by invisible tennis balls!