Ideal Gas Law
Relates pressure, volume, moles, and temperature of a gas.
Formula
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Example
Cornerstone of gas behavior
How it works
The ideal gas law links the four macroscopic features of a gas: how much gas there is, how tightly it is squeezed, how much space it occupies, and how hot it is. It comes from combining the experimental relationships of Boyle’s law, Charles’s law, and Avogadro’s law into one equation that works well when gas particles are far enough apart that their own volume and attractions can be neglected. Because temperature must be measured on an absolute scale, the law uses kelvin rather than degrees Celsius.
When to use it
Use this when you need to find one gas variable from the other three, such as calculating the amount of gas in a flask, predicting the pressure change in a sealed container, or finding how much a gas expands when heated. It is especially useful in chemistry labs, gas stoichiometry, and problems involving balloons, syringes, and reaction vessels.
Worked example, step by step
A sample of gas has a pressure of 95.0 kPa, a volume of 2.50 L, and a temperature of 300 K. Find the number of moles, n. Use PV = nRT Rearrange to n = PV / RT Substitute the values: n = (95.0 kPa × 2.50 L) / (8.314 kPa·L·mol⁻¹·K⁻¹ × 300 K) Calculate the numerator: 95.0 × 2.50 = 237.5 kPa·L Calculate the denominator: 8.314 × 300 = 2494.2 kPa·L·mol⁻¹ n = 237.5 / 2494.2 = 0.0952 mol Final answer: n ≈ 0.095 mol
Common mistakes to avoid
- Using degrees Celsius instead of kelvin for temperature
- Mixing units for the gas constant without matching pressure and volume units
- Forgetting to rearrange the formula correctly before substituting values
Did You Know?
One mole of any ideal gas fills about 22.4 litres at standard conditions, regardless of which gas it is.
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