Internal energy, heating and cooling curves, and why the temperature stops rising while a substance melts or boils.
What you will learn
- Say what internal energy is
- Read melting and boiling points from heating and cooling curves
- Explain the flat parts of a heating curve
Energy stored by particles
The particles in a substance have kinetic energy (they move) and potential energy (from the forces holding them together).
Together these are its internal energy.
Heating a substance raises its internal energy. Either:
- the particles move faster, so the temperature rises, or
- the bonds between them are broken, so the state changes, with no change in temperature.
Changes of state are physical changes: the mass stays the same and the change can be reversed. (A chemical change makes a new substance, and usually cannot be reversed.)
Temperature depends on the average kinetic energy of the particles. So while the state changes, the kinetic energy and the temperature stay the same; the energy supplied raises the potential energy instead.
The changes have names:
- melting: solid to liquid; freezing: liquid to solid
- boiling or evaporating: liquid to gas; condensing: gas to liquid
- subliming: solid straight to gas
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Energy stored by particles
- Reading a heating curve
- Try it: Read the graph
9 practice questions, marked as you go; about 20 minutes in all.
Key terms
Internal energy, Temperature, State, Boiling, Cooling curve
In this unit: Particle model, density and gas pressure
Density and its required practical, changes of state, specific latent heat, and the particle model of gas pressure, including p₁V₁ = p₂V₂.