Particle Model of Matter

Think of everything around you as being made of tiny invisible particles - that's exactly what the particle model shows us! This model explains why solids, liquids, and gases behave so differently.

Density is basically how tightly packed these particles are. It's calculated as mass divided by volume $ρ = m/V$, measured in kg/m³. Imagine a crowded lift versus an empty playground - that's the difference between high and low density.

In solids, particles are packed closely together with strong forces holding them in a regular structure. They can't move around or flow, and you can't compress them. Liquids have particles that are close but with gaps, weaker forces, and can flow but still can't be compressed. Gases have particles far apart with weak forces, constant random motion, and can be compressed and expand to fill any container.

Quick Tip: Remember the crowd analogy - solids are like a packed concert, liquids like people walking through a shopping centre, and gases like people scattered across a massive field!

Internal Energy and State Changes

Your hot cup of tea has internal energy - this is all the energy stored by particles in their movement (kinetic) and position (potential). When you heat something, you're adding to this internal energy store.

Here's what's brilliant: when substances change state, the temperature stays constant even though you're adding energy! During melting, boiling, or freezing, all that energy goes into breaking or forming bonds between particles instead of making them move faster.

Internal energy increases when solids melt to liquids, liquids boil to gases, or solids sublimate directly to gases. It decreases during freezing, condensation, and deposition. Think of it like this - particles need energy to break free from each other, just like you need energy to break free from a group hug!

The temperature change depends on the mass of substance, type of material, and how much energy you put in. More mass or less energy input means smaller temperature changes.

Remember: During state changes, temperature stays constant while internal energy changes - it's like all the energy is busy breaking particle bonds rather than heating up!

Specific Heat Capacity and Latent Heat

Specific heat capacity (SHC) tells you how much energy you need to heat up 1kg of a material by 1°C. Different materials need different amounts - water needs loads of energy, which is why it takes ages to boil a kettle!

The equation is: Change in energy = mass × specific heat capacity × temperature change. This explains why a small amount of hot oil can burn you badly (low SHC means it releases lots of energy quickly), whilst a large amount of warm water might not.

Specific latent heat (SLH) is the energy needed to change state without changing temperature. There are two types: latent heat of fusion (solid ↔ liquid) and latent heat of vaporisation (liquid ↔ gas). The equation is: Q = mL.

Vaporisation always needs more energy than fusion - it takes much more energy to turn water into steam than to melt ice. That's why steam burns are so dangerous!

Real-world connection: This is why sweating cools you down - your body heat provides the latent heat of vaporisation to turn sweat into water vapour!

Gas Pressure and Volume Laws

Gas pressure comes from particles constantly hitting container walls - more hits or harder hits means higher pressure. Atmospheric pressure is about 101,000 Pa (or 101 kPa), which is like having a 10kg weight pressing on every square centimetre!

Boyle's Law shows that pressure and volume are inversely proportional when temperature stays constant. Double the pressure, and volume halves: P₁V₁ = P₂V₂. Imagine squashing a balloon - as you reduce its volume, the pressure inside increases.

Pressure Law tells us that pressure is directly proportional to absolute temperature: P₁/T₁ = P₂/T₂. Remember to always use Kelvin for temperature calculations! To convert: Kelvin = Celsius + 273.

These laws work because they're all about particle movement. Higher temperature means faster-moving particles hitting walls harder. Less volume means particles hit walls more often. It's like having more energetic people in a smaller room!

Exam tip: Always convert Celsius to Kelvin for gas law calculations - just add 273 to your Celsius temperature!