Charles Law
At constant pressure, volume is proportional to temperature.
Formula
Variables
Example
Heated gas expands
How it works
Charles’s law says that if the pressure stays the same, a gas takes up more space when it gets hotter and less space when it gets colder. This happens because higher temperature means gas particles move faster, so they spread out more unless pressure changes to force them together. The temperatures must be measured on the Kelvin scale, because the relationship depends on absolute thermal energy, not Celsius values.
When to use it
Use this when a gas is being heated or cooled while the pressure is held constant, such as in a balloon, a gas syringe, or a weather balloon. It is useful for finding how a gas’s volume changes when temperature changes at steady pressure.
Worked example, step by step
A gas has a volume of 2.5 L at 300 K. What volume will it have at 360 K if the pressure stays constant? Use Charles’s law: V1 / T1 = V2 / T2 Substitute the values: 2.5 / 300 = V2 / 360 Solve for V2: V2 = (2.5 × 360) / 300 V2 = 900 / 300 V2 = 3.0 L Final answer: the gas will expand to 3.0 L.
Common mistakes to avoid
- using Celsius instead of Kelvin for temperature
- forgetting that the pressure must stay constant
- mixing up the starting and ending values when rearranging the formula
Did You Know?
Charles's law is why a balloon shrivels in the freezer and puffs back up in the warmth.
Share this formula
More in Chemistry
View allIdeal Gas Law
IntermediateRelates pressure, volume, moles and temperature of a gas.
Molarity
BasicConcentration in moles of solute per litre of solution.
Moles from Mass
BasicNumber of moles from mass and molar mass.
pH
BasicAcidity from hydrogen-ion concentration.
pOH
BasicBasicity from hydroxide-ion concentration.
Henderson–Hasselbalch
AdvancedpH of a buffer solution.