Ideal Gas Law
Relates pressure, volume, moles and temperature of a gas.
Formula
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Example
One mole of gas at 0 °C and 1 atm occupies 22.4 L (PV = nRT).
How it works
The ideal gas law combines the individual gas relationships into one useful equation: a gas takes up more volume when you add more particles or heat it up, and less volume when you squeeze it or cool it down. It works best when a gas is dilute and the particles are far enough apart that their own size and intermolecular forces are negligible, which is a good approximation for many gases at moderate pressure and temperature.
When to use it
Use this law when you need to find pressure, volume, amount of gas, or temperature for a gas sample, especially in chemistry and physics problems involving containers, balloons, syringes, or reaction gases. It is also useful for converting between known gas quantities in lab calculations.
Worked example, step by step
A 2.50 mol sample of gas is kept at 27.0 °C in a 10.0 L container. What is the pressure? Step 1: Convert temperature to Kelvin: T = 27.0 + 273.15 = 300.15 K Step 2: Write the ideal gas law: PV = nRT Step 3: Solve for pressure: P = nRT / V Step 4: Substitute values: P = (2.50 mol)(8.314 J/mol·K)(300.15 K) / 10.0 L Step 5: Calculate: P = 6236 Pa Step 6: Final answer: P ≈ 6.24 × 10^3 Pa = 6.24 kPa
Common mistakes to avoid
- Using Celsius instead of Kelvin for temperature
- Mixing units so that R does not match the pressure and volume units
- Forgetting to rearrange the equation correctly before substituting values
Did You Know?
The ideal gas law combines three older laws into one, and works because gas molecules are mostly empty space.
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