Idea 8of 9Builds onThe price per degree
The thermometer stops
Ice melts at zero with the burner on. Why no rise?
Today you'll discover
- what a flat piece of the curve means
- where the energy goes while the reading stays
- the much bigger bill at boiling
Think firstIce melting at 0 °C, burner on, reading stuck
The burner adds energy, yet the thermometer stays at 0 °C while the ice melts. Where is the energy going?
Decide first, then press Next. Compare the lengths of the two flat pieces.
A heating curve with a short flat piece at zero degrees. After a prediction, the flat piece is labelled with the melting energy, then a much longer flat piece at one hundred degrees appears for boiling, and both are named. The last step asks why steam burns worse than boiling water.
See the whole ideathe big idea and the key word, in one place
The big idea
A change of state costs energy, with no rise.
Easy to get wrongA flat reading with the burner on does not mean no energy is going in. It means the energy is buying a change of state.
Key word
- latent heat
- the energy per kilogram to change a substance's state at constant temperature: Q = m L; of fusion for melting, of vaporization for boiling
About this modelDrawn to scale: boiling costs about seven times what melting costs, per kilogram.
Drawn to scale: boiling costs about seven times what melting costs, per kilogram.
Ready to use it?
- Choose m c ΔT or m L for a described heating step, and find the energy.