Internal Energy and Heating

Think of internal energy as the total energy budget that all particles in a substance have stored up. Every particle is constantly jiggling about (kinetic energy) and has energy due to its position relative to other particles (potential energy).

When you heat something up, you're pumping more energy into this system, which increases the internal energy. Usually this makes the temperature rise, but the amount depends on three key factors: how much stuff you're heating, what it's made of, and how much energy you're adding.

Here's where it gets interesting - sometimes you can keep adding heat without the temperature changing at all! This happens during melting and boiling when the extra energy goes towards breaking the bonds between particles instead of making them move faster.

Quick Tip: Look for flat horizontal lines on heating graphs - these show energy being added but temperature staying constant during state changes.

Specific Latent Heat

When substances condense or freeze, the opposite happens - particles form new bonds and release energy. The internal energy decreases, but again the temperature stays constant until the change of state is complete.

Latent heat is the energy needed to change a substance's state without changing its temperature. It's like the entry fee particles pay to switch between being solid, liquid, or gas.

Specific latent heat makes this more precise - it's exactly how much energy you need to change 1kg of a substance from one state to another. Different materials need different amounts, and it varies depending on which states you're switching between.

There are two main types: specific latent heat of fusion (solid ↔ liquid) and specific latent heat of vaporisation (liquid ↔ gas). The handy formula to remember is E = ML, where E is energy, M is mass, and L is specific latent heat.

Exam Tip: Remember that vaporisation usually requires much more energy than fusion - that's why steam burns are so dangerous!