Gas Law Examples: Solved Step-by-Step

Practice with these fully worked gas law problems. Each example shows the formula, substitution, and final answer.

Ideal Gas Law Examples (PV = nRT)

Example 1: Find Pressure

Problem: 3.0 moles of an ideal gas occupy 15.0 L at 350 K. What is the pressure in atm?

Example 2: Find Volume at STP

Problem: What volume does 2.5 mol of gas occupy at STP (1 atm, 273.15 K)?

Example 3: Find Moles

Problem: A 8.0 L tank at 4.0 atm and 400 K. How many moles of gas are inside?

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Combined Gas Law Examples

Example 4: Find Final Pressure

Problem: A gas at 1.0 atm, 4.0 L, 300 K is compressed to 2.0 L and heated to 450 K. Find P₂.

Example 5: Find Final Volume

Problem: P₁ = 3.0 atm, V₁ = 2.0 L, T₁ = 250 K, P₂ = 1.5 atm, T₂ = 500 K. Find V₂.

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Boyle's Law Examples

Example 6: Compressing a Gas

Problem: A gas at 1.0 atm occupies 10.0 L. What is the pressure if compressed to 2.5 L?

Example 7: Expanding a Gas

Problem: A gas at 5.0 atm in a 3.0 L container. What volume at 1.0 atm?

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Charles's Law Examples

Example 8: Heating a Gas

Problem: A gas occupies 5.0 L at 300 K. What volume at 600 K?

Example 9: Converting °C to K

Problem: V₁ = 2.0 L at 20°C. Find V₂ at 80°C.

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Gay-Lussac's Law Example

Example 10: Heating a Sealed Container

Problem: A sealed can has P₁ = 1.0 atm at 300 K. What is the pressure at 450 K?

Example 11: Cooling a Sealed Container

Problem: A rigid tank holds gas at 4.0 atm and 500 K. The tank cools to 250 K. Find P₂.

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Dalton's Law Examples

Example 12: Total Pressure of a Gas Mixture

Problem: A mixture contains 0.50 atm N₂, 0.30 atm O₂, 0.15 atm Ar. Find P_total.

Example 13: Finding a Partial Pressure from Mole Fraction

Problem: A gas mixture at 2.0 atm total pressure contains 40% O₂ by moles. Find the partial pressure of O₂.

Try in Dalton's Law Calculator →

Avogadro's Law Example

Example 14: Doubling the Moles

Problem: A container holds 2.0 mol of gas occupying 44.8 L at constant T and P. If 3.0 more moles are added (total 5.0 mol), what is the new volume?

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Tips for Solving Gas Law Problems

1. Identify the law: Determine which variables are given and what is constant. This tells you which gas law to use.
2. Convert to Kelvin: All gas law calculations require absolute temperature. K = °C + 273.15. Never use °C or °F directly in formulas.
3. Check unit consistency: Make sure pressure and volume units match the R constant you are using. If unsure, convert everything to atm and liters and use R = 0.08206.
4. Rearrange before substituting: Solve the formula algebraically for the unknown variable first, then plug in numbers. This reduces arithmetic errors.
5. Sanity check your answer: Does the result make physical sense? If you compressed a gas, the pressure should increase. If you heated a gas at constant pressure, the volume should increase.

Use our Gas Law Formulas reference to quickly find the right equation. For unit guidance, see PV=nRT Units.