Relate pressure, volume, and temperature for a gas using Boyle's, Charles's, and the combined and ideal gas laws — nearly every problem is the same algebra with a different pair of variables held constant. Every question comes with a written walkthrough of which law applied and why.
Every gas law formula requires temperature in Kelvin — plugging in a Celsius value directly, especially a negative one, produces a nonsensical or wildly incorrect result.
Boyle's Law only holds pressure and volume in an inverse relationship when temperature stays fixed — if temperature also changes in the problem, the combined gas law is needed instead.
Boyle's Law is inverse (pressure up, volume down) while Charles's Law is direct (volume up, temperature up) — applying the wrong direction flips the answer to its reciprocal.
Straight from the bank — one per difficulty tier. Reveal the answer to see the explanation you'd get in a real session.
A gas occupies 4.0 L at a pressure of 2.0 atm. If the pressure increases to 8.0 atm at constant temperature, what is the new volume?
A — 1.0 L. Boyle's Law: P₁V₁ = P₂V₂, so (2.0)(4.0) = (8.0)V₂, giving V₂ = 8/8 = 1.0 L. 16 L (B) comes from treating pressure and volume as directly proportional instead of inversely proportional — multiplying instead of solving the inverse relationship.
A gas has a volume of 3.0 L at 27°C. If the volume increases to 4.0 L at constant pressure, what is the new temperature in Celsius?
A — 127°C. Convert to Kelvin first: 27°C = 300K. Apply Charles's Law: 3.0/300 = 4.0/T₂, giving T₂ = 400K. Converting back: 400 − 273 = 127°C. 400°C (B) comes from solving correctly in Kelvin but forgetting to convert the final answer back to Celsius, reporting the Kelvin value as if it were already in Celsius.
A sealed container holds a gas at 1.5 atm, 2.0 L, and 250K. If the gas is compressed to 1.0 L and heated to 400K, what is the new pressure?
A — 4.8 atm. Apply the combined gas law: P₁V₁/T₁ = P₂V₂/T₂, so (1.5)(2.0)/250 = P₂(1.0)/400. That gives 0.012 = P₂/400, so P₂ = 0.012 × 400 = 4.8 atm. 0.012 atm (C) stops at the intermediate ratio and reports it directly, forgetting to multiply through by 400 to isolate P₂.
Gas law problems reward identifying which variable is held constant before choosing a formula — get that right and the algebra rearranges itself.
Before touching a formula, convert any Celsius temperature to Kelvin and name which of pressure, volume, or temperature stays fixed. Untimed practice is where that setup habit sticks.
Move to timed sessions once formula selection and Kelvin conversion are both automatic.
Pair gas laws with chemical reactions in a mock — stoichiometry problems often combine a balanced equation with a gas law.
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