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Charles's law
Beginner
At fixed pressure, volume is proportional to temperature.
V/T = constAt constant pressure, V/T = constant (T in kelvin). Volume goes to zero at −273 °C when extrapolated.
A balloon at 300 K heated to 330 K grows 10%.
Use kelvin, not °C.
In more detail
Charles's law states that for a fixed amount of gas at constant pressure, volume is proportional to absolute temperature, V/T = constant.
Real-world uses
- Hot air balloons expand as they are heated, reducing their density.
- Balloons shrink when put in a freezer.
- A balloon left in a warm car expands, showing that the volume of a gas at constant pressure is proportional to its temperature.
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Frequently asked questions
Why must temperature be in kelvin?
Because proportionality only holds when the zero point is absolute zero.
What does it predict at absolute zero?
A volume of zero, which real gases never reach because they condense first.
Why must the temperature be in kelvin?
Charles's law is a direct proportionality, which only holds when the temperature is measured from absolute zero.
Related topics in Heat & Thermodynamics
Blackbody radiation · Ideal gas laws · Boyle's law · Ideal gas equation · Avogadro's number · Internal energy