Absolute zero
2 marks · NormalWhy must you convert temperatures to kelvin before using gas law equations?
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Because Kelvin temperature is proportional to the pressure/volume of a gas and starts from absolute zero, so gas law equations are only valid with kelvin.
Also accept: Kelvin scale starts from absolute zero and is proportional to particle kinetic energy; gas law equations require temperature measured from absolute zero.
Common mistakes: Saying Kelvin is just another scale without stating the reason for gas laws.
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Marking points
B1 · 1 mark · Mentions that gas law equations require temperature measured from absolute zero (Kelvin), not Celsius.
B1 · 1 mark · Explains that pressure and volume are proportional to absolute (Kelvin) temperature, not Celsius.
Worked solution
The Kelvin scale starts at absolute zero, where particle motion theoretically stops. Gas laws rely on temperature being proportional to kinetic energy, so you must use Kelvin—otherwise, the equations would give wrong answers or non-physical results at negative Celsius temperatures.