Beginner Topic 228 of 1102 States of Matter & Solutions
Charles's Law
At constant pressure, gas volume is directly proportional to its absolute temperature.
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In-depth explanation of Charles's Law
Charles's law states that at constant pressure and fixed amount of gas, the volume is directly proportional to the absolute temperature in kelvin, so V/T is constant. Heating a gas increases the average kinetic energy of its particles, which strike the walls with greater force and push the boundary outward. Extrapolating the straight line of V against T predicts zero volume at -273.15°C, which led to the concept of absolute zero. Temperature must always be in kelvin for this direct proportionality to hold, and V1/T1 = V2/T2 applies directly. Hot-air balloons rise because heating lowers the density of the air inside them.
Going deeper: Charles's Law
Key ideas: Use V1/T1 = V2/T2 with temperature in kelvin and fixed pressure and moles. Volume changes by about 1/273 of its 0 C value per degree. A rule of thumb is that doubling absolute temperature doubles volume. Plots of V against T in Celsius cross the temperature axis at -273.15 C.
Common mistakes and connections: The most frequent mistake is using Celsius temperatures, which gives nonsense; doubling 20 C is not 40 C in this context. Another is assuming real gases reach zero volume at absolute zero; they liquefy first. Links to absolute zero, the combined gas law, density changes with temperature and the buoyancy of balloons.
Visualization of Charles's Law
At constant pressure the volume of a gas rises linearly with absolute temperature, extrapolating to zero volume at -273.15 C. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A balloon with a volume of 1.00 L at 300 K, heated to 330 K at constant pressure, expands to 1.10 L.
Frequently asked questions about Charles's Law
What is Charles's Law?
At constant pressure, gas volume is directly proportional to its absolute temperature.
Is Charles's Law a beginner, intermediate or advanced topic?
Charles's Law is a beginner topic in States of Matter & Solutions. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Charles's Law?
Study these earlier topics in States of Matter & Solutions first: Barometer, Standard Temperature and Pressure, Boyle's Law.
What comes after Charles's Law?
The next topics in States of Matter & Solutions are Gay-Lussac's Law and Avogadro's Law.
Can I practise Charles's Law with quizzes?
Yes. The interactive lesson includes a self-check question on Charles's Law, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Charles's Law fits in States of Matter & Solutions
Charles's Law is topic 9 of 109 in States of Matter & Solutions.