Free tool
Pick the unknown, enter the other three values in whatever units the problem gives, and get pressure, volume, moles or temperature from PV = nRT with every conversion shown.
Built for General Chemistry IThe unit next to the unknown sets the unit of the answer. R = 0.082057 L·atm/(mol·K), usually rounded to 0.08206.
Enter the three known values.
Gas law problems are mostly unit conversions done in the right order. Encodr keeps them on a spaced-repetition schedule so the setup is automatic by exam day.
Get started freeThe ideal gas law ties together pressure (P), volume (V), amount in moles (n) and absolute temperature (T):
PV = nRT. With R = 0.08206 L·atm/(mol·K), P must be in atm, V in liters and T in kelvin.
This calculator uses R = 0.082057 internally and converts for you: 1 atm = 101.325 kPa = 760 mmHg = 760 torr,
1 L = 1000 mL, and K = °C + 273.15. Temperatures at or below 0 K are rejected, since absolute zero is the floor.
Worked example: 0.500 mol of gas in a 10.0 L container at 25 °C. First T = 25 + 273.15 = 298.15 K. Then P = nRT ÷ V = (0.500)(0.08206)(298.15) ÷ 10.0 = 1.22 atm. Plugging in 25 instead of 298.15 gives 0.103 atm, the most common wrong answer.
At STP (273.15 K and 1 atm, the convention OpenStax uses), 1.00 mol of an ideal gas takes up about 22.4 L. Real gases drift from ideal behavior at high pressure and low temperature. More examples, including molar mass from gas data: the ideal gas law with worked examples. Practice: the free General Chemistry I flashcards.
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