Ideal Gas Law
PV = nRT
The ideal gas law relates pressure, volume, amount, and temperature of an ideal gas. It combines Boyle's, Charles's, and Avogadro's laws into one equation and is fundamental for gas calculations.
Variables
Gas pressure in atm, kPa, or mmHg
Gas volume in liters
Amount of gas in moles
0.0821 L·atm/(mol·K) or 8.314 J/(mol·K)
Absolute temperature in Kelvin
Example Calculation
Scenario
A 2.50 L container holds 0.100 mol of gas at 25°C. Calculate the pressure.
Given Data
Calculation
P = nRT/V = (0.100 mol)(0.0821 L·atm/mol·K)(298 K)/(2.50 L)
Result
P = 0.979 atm
Interpretation
The gas exerts approximately 1 atmosphere of pressure, which is close to standard atmospheric pressure.
When to Use This Formula
- ✓Calculating any gas variable when three others are known
- ✓Finding moles of gas at given conditions
- ✓Determining volume at STP
- ✓Gas stoichiometry calculations
Common Mistakes
- ✗Forgetting to convert temperature to Kelvin
- ✗Using the wrong R value for the units
- ✗Not checking that units cancel properly
- ✗Applying to real gases at high P or low T
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Common questions about this formula
The ideal gas law breaks down at high pressures (molecules close together) and low temperatures (near condensation). Use the van der Waals equation for more accurate results with real gases under these conditions.
Use R = 0.0821 L·atm/(mol·K) when pressure is in atm and volume in L. Use R = 8.314 J/(mol·K) when working with energy units or when pressure is in Pa and volume in m³.