Ideal Gas Law (PV = nRT): Steps, Units and Examples
Solve gas problems with PV = nRT: pick R, convert to kelvin, and watch your units, with two worked chemistry examples.
The equation
- PV = nRT
- R = 0.0821 L·atm / (mol·K)
P in atm, V in liters, n in moles, T in kelvin.
Before you plug in
- Convert °C to K: K = °C + 273
- Match units to R
- Solve for the unknown
Temperature must be in kelvin every time.
Example 1
0.50 mol of gas is in a 10. L container at 300 K. Find the pressure.
- P = nRT / V
- = (0.50)(0.0821)(300) / 10.
P ≈ 1.2 atm
Example 2
What volume does 1.0 mol of gas occupy at 1.0 atm and 273 K?
- V = nRT / P
- = (1.0)(0.0821)(273) / 1.0
V ≈ 22 L
Common mistake
T = 27 (in °C)
Always convert to kelvin: 27 °C = 300 K.
If pressure is in kPa or mmHg, convert it or use the matching R.
Volume must be in liters with R = 0.0821.
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