Gas Laws
Calculator
PV=nRT, Boyle, Charles and Avogadro — unit conversion and step-by-step solutions.
Enter three values — the fourth is calculated automatically
What Are Gas Laws?
Gas laws describe how pressure (P), volume (V), temperature (T) and amount (n) of a gas are related. Boyle's law gives the inverse relationship between pressure and volume at constant temperature; Charles's law relates volume and absolute temperature at constant pressure; Avogadro's law relates volume and amount at constant pressure and temperature.
Combining these three laws yields the ideal gas law PV = nRT. This equation is among the most frequently tested formulas in high-school chemistry.
Gas Law Formulas
Ideal Gas Law
General relationship among pressure, volume, amount and temperature. Combines Boyle, Charles and Avogadro laws.
R = 8.314 J/(mol·K) | R = 0.082 L·atm/(mol·K)Boyle's Law
At constant temperature, pressure and volume are inversely proportional. Higher pressure → lower volume.
Condition: T constant, n constantCharles's Law
At constant pressure, volume is directly proportional to absolute temperature. Higher T → higher V.
Condition: P constant, n constant | T must be in KelvinAvogadro's Law
At constant P and T, volume is directly proportional to amount. 1 mol ideal gas occupies 22.4 L at STP.
Condition: P constant, T constantExample Problems
2 mol of N₂ at 300 K in a 5 L container. What is the pressure in atm?
A gas at 3 atm and 8 L expands to 12 L at constant temperature. What is the new pressure?
A gas with 5 L at 273 K is heated to 546 K at constant pressure. What is the new volume?
At STP, 1 mol of gas occupies 22.4 L. What volume does 3 mol occupy under the same conditions?
Frequently Asked Questions
What is the ideal gas law (PV=nRT)?
The ideal gas law relates pressure (P), volume (V), amount (n) and temperature (T): PV = nRT, where R is the universal gas constant. It combines Boyle, Charles and Avogadro laws and is the most used gas equation in high-school chemistry.
What is Boyle's law and how is it applied?
Boyle's law states that at constant temperature, pressure and volume are inversely proportional: P₁V₁ = P₂V₂. For example, if a gas at 2 atm and 5 L is compressed to 4 atm at constant temperature, the volume becomes 2.5 L.
What is Charles's law?
Charles's law states that at constant pressure, volume is directly proportional to absolute temperature (Kelvin): V₁/T₁ = V₂/T₂. Celsius cannot be used in the ratio because T cannot be zero. Higher temperature means larger volume.
What is Avogadro's law?
Avogadro's law states that at constant pressure and temperature, volume is directly proportional to amount: V₁/n₁ = V₂/n₂. At STP (0°C, 1 atm), 1 mol of any ideal gas occupies 22.4 L.
What value does R take?
R depends on units. In SI (Pa, m³): R = 8.314 J/(mol·K). With pressure in atm and volume in L: R = 0.082057 L·atm/(mol·K). This calculator converts automatically between unit systems.
Why must temperature be in Kelvin?
In Charles's law and the ideal gas equation, temperature appears in the denominator, so T cannot be zero. Proportional relationships require an absolute scale: T(K) = T(°C) + 273.15. This tool converts °C input to Kelvin automatically.
What are STP conditions?
STP (Standard Temperature and Pressure) is 0°C (273.15 K) and 1 atm (101,325 Pa). In many curricula, 1 mol of ideal gas occupies 22.4 L at STP. Use the STP button in the calculator to fill these values quickly.
What is the difference between ideal and real gases?
An ideal gas ignores intermolecular forces and molecular volume. Real gases deviate at high pressure and low temperature; the van der Waals equation is then used. In high-school chemistry, gases are usually treated as ideal.
About the Gas Laws Calculator
Boyle's law describes the inverse relationship between pressure and volume (P₁V₁ = P₂V₂). Charles's law relates temperature and volume (V₁/T₁ = V₂/T₂). Avogadro's law states that volume increases with amount (V₁/n₁ = V₂/n₂). Together they form the ideal gas law PV = nRT, which solves most introductory gas problems. This tool supports atm, Pa, kPa, mmHg, bar, L, mL, m³, Kelvin and Celsius for exam preparation.