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Heat a beaker of ice-water and, for a while, the thermometer refuses to move at all — even though you’re still pumping energy in continuously. Understanding exactly where that energy is going, when it isn’t raising temperature, is the key to this whole topic.
What you'll be able to do
The of a substance is the sum of the random kinetic and potential energies of all its particles. Kinetic energy comes from particles’ constant random motion; potential energy comes from the bonds between them, which can stretch, break or form.
(0 K, C) is the theoretical temperature at which particles have minimum kinetic energy.
Tip — Kelvin and Celsius share the same size degree — only the zero point differs: T(K) = θ(°C) + 273.
, , is the energy required to raise the temperature of 1 kg of a substance by 1 K, in J kg⁻¹ K⁻¹.
During a change of state, energy is transferred, but temperature stays — all the energy goes into breaking (or forming) bonds, changing potential energy, not kinetic energy. The applies to melting/freezing; the applies to boiling/condensing, and is always larger, since boiling must separate particles completely.
Tip — A multi-step heating problem always alternates between mcΔθ (temperature changing) and mL (state changing, constant temperature) — never combine the two into a single calculation.
Equation recap
Common mistakes to avoid
Key takeaways
Test yourself
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