Charles's Law states that volume and temperature are directly proportional at constant pressure. Heat a gas and it expands; cool it and it contracts.
V₁ / T₁ = V₂ / T₂
Initial volume / initial temperature = Final volume / final temperature
ALWAYS convert °C or °F to Kelvin before using Charles's Law. Using Celsius will give completely wrong answers!
K = °C + 273.15
Example: 25°C = 298.15 K (often rounded to 298 K)
V ∝ T (at constant P and n)
Common Units: L, mL, cm³, m³
Volume before the temperature change
Units: K (Kelvin) - MUST USE KELVIN!
Temperature before the change
❌ Do NOT use °C or °F directly!
Units: Same as V₁
Volume after the temperature change
Units: K (Kelvin) - MUST USE KELVIN!
Temperature after the change
Pressure (P) must remain constant
Amount of gas (n) must remain constant
No gas can enter or leave the system
V₂ = V₁T₂ / T₁
Most common use!
T₂ = V₂T₁ / V₁
V₁ = V₂T₁ / T₂
T₁ = V₁T₂ / V₂
T₁ = 20 + 273 = 293 K
T₂ = 80 + 273 = 353 K
V₁/T₁ = V₂/T₂
V₂ = V₁T₂ / T₁
V₂ = (2.50 L)(353 K) / (293 K)
V₂ = 882.5 L·K / 293 K = 3.01 L
Answer: V₂ = 3.01 L
✅ Makes sense: Temperature increased by 20%, volume increased by 20%
Heat the air inside → volume tries to expand → since balloon is open, air escapes → lower density → balloon rises!
Take balloon from warm house to cold outdoors → temperature drops → volume decreases → balloon deflates
Cold ball feels flat (V decreased), warm ball feels firm (V increased) - though pressure also changes
Compress air rapidly → temperature skyrockets (adiabatic) → demonstrates inverse of Charles's Law
THE #1 MISTAKE! Temperature MUST be in Kelvin. Using °C gives completely wrong answers. Always convert: K = °C + 273.
Charles's Law ONLY works when pressure is constant. If P changes, use the Combined Gas Law instead.
V₁ and V₂ must be in the same units. T₁ and T₂ must BOTH be in Kelvin. Convert before calculating!
If temperature increases, volume MUST increase. If temperature decreases, volume MUST decrease. Verify your answer makes physical sense!
V₁/T₁ = V₂/T₂ at constant pressure. Volume and temperature are directly proportional - when one goes up, the other goes up.
Charles's Law requires an absolute temperature scale. 0 K is absolute zero - no molecular motion. Using °C would incorrectly suggest gas has zero volume at 0°C!
Higher temperature = faster molecular motion = molecules hit walls harder and more often. At constant pressure, container must expand to accommodate the increased kinetic energy.
Theoretically, volume would be zero. In reality, gases liquefy or solidify before reaching 0 K, so the law breaks down at very low temperatures.
Boyle's Law: P and V (T constant) - inverse relationship. Charles's Law: V and T (P constant) - direct relationship. Different variables!