This topic accounts for approximately 7% of your exam marks.
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Gas law calculations (Boyle's Law, pressure-temperature) and kinetic theory explanations appear regularly.
What "temperature" really measures
Temperature is a measure of the average kinetic energy of the particles in a substance
Hotter substance means particles moving on average faster, which means higher average kinetic energy
The link is proportional when temperature is measured in kelvin:
T (in K) ∝ average kinetic energy of particles
This is why Kelvin is the right scale for gas laws: doubling the Kelvin temperature genuinely doubles the average kinetic energy of the molecules. Doubling the Celsius temperature does not: going from 1 °C to 2 °C is only 0.36 % more average kinetic energy
Why all states show this behaviour
The temperature–KE link applies to every state of matter:
in a gas, almost all the internal energy sits in the kinetic store (molecules barely interact), so KE and temperature are tightly linked
in a solid, most of the kinetic energy is vibrational rather than translational, but the rule still holds, so hotter solids vibrate harder
in a liquid, similarly, particles slide past each other faster as the temperature climbs
Evaporation cools the liquid that's left behind
When a liquid evaporates, only the most energetic surface molecules can break free of the intermolecular bonds and escape as vapour
The molecules left behind have a lower average kinetic energy than before
Lower average KE means lower , so the remaining liquid cools
This is the physics behind sweating, why a wet swimsuit feels cold in a breeze, and why fridges and air conditioners use an evaporating refrigerant to extract heat