Charles's Law
Volume is proportional to temperature at constant pressure.
Formula
Variables
Example
Gas at 2 L and 300 K warmed to 600 K expands to 4 L at constant pressure.
How it works
Charles’s Law says that for a fixed amount of gas kept at constant pressure, the gas’s volume changes in direct proportion to its absolute temperature. Heating a gas makes its particles move faster, so they need more space to maintain the same pressure; cooling does the opposite. This only works when temperature is measured in kelvin, because the proportional relationship depends on an absolute temperature scale.
When to use it
Use this when a gas is heated or cooled while the pressure stays the same, such as in balloons, weather balloons, or sealed gas samples that can expand freely. It is also useful for predicting how gas volume changes in lab problems involving temperature changes at constant pressure.
Worked example, step by step
A balloon contains 1.5 L of gas at 250 K. It is warmed to 400 K at constant pressure. What is the new volume? Step 1: Write the law: V1/T1 = V2/T2 Step 2: Substitute the known values: 1.5/250 = V2/400 Step 3: Solve for V2: V2 = (1.5 × 400) / 250 Step 4: Calculate: V2 = 600 / 250 = 2.4 Final answer: The new volume is 2.4 L.
Common mistakes to avoid
- Using degrees Celsius instead of kelvin
- Forgetting that pressure must stay constant
- Reversing the variables and solving for the wrong volume or temperature
Did You Know?
Charles's law is why a balloon shrinks when taken out into the cold.
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.