The Gas Laws — Practice · Grade 11 Science

Chapter: States of Matter & Gases

What this practice covers

By the end of The Gas Laws you should be able to:

11 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: Boyle's Law, Charles's Law, Gay-Lussac's Law, combined gas law, Kelvin scale, absolute zero, pressure.

Problem 1

Boyle's Law states that at constant temperature, the pressure and volume of a gas are…
  1. completely unrelated
  2. inversely proportional
  3. directly proportional
  4. always equal
Answer and explanation

inversely proportional

Boyle's Law: as volume decreases, pressure increases in inverse proportion, so P₁V₁ = P₂V₂.

Problem 2

A gas occupies 6.0 L at 1.0 atm. At constant temperature, what is its volume when the pressure is raised to 3.0 atm?
Answer and explanation

2 L

Boyle's Law: V₂ = P₁V₁/P₂ = (1.0 × 6.0)/3.0 = 2.0 L.

Problem 3

A gas at 200 K occupies 4.0 L. At constant pressure, what volume does it occupy at 300 K?
Answer and explanation

6 L

Charles's Law: V₂ = V₁ × (T₂/T₁) = 4.0 × (300/200) = 6.0 L.

Problem 4

A gas in a rigid, sealed tank exerts 2.0 atm at 300 K. What pressure does it exert when heated to 600 K?
Answer and explanation

4 atm

Gay-Lussac's Law (constant volume): P₂ = P₁ × (T₂/T₁) = 2.0 × (600/300) = 4.0 atm.

Problem 5

Why must every temperature be converted to kelvin before it is used in a gas law?
Answer and explanation

The gas laws describe direct proportionality with the true amount of particle motion, and only the Kelvin scale starts at absolute zero (genuine zero energy). Celsius has an arbitrary zero and negative values, so ratios like V/T come out wrong unless temperatures are first converted with K = °C + 273.

Problem 6

A gas occupies 3.0 L at 1.0 atm and 300 K. Using the combined gas law, what volume does it occupy at 2.0 atm and 450 K?
Answer and explanation

2.25 L

Combined gas law: V₂ = V₁ × (P₁/P₂) × (T₂/T₁) = 3.0 × (1.0/2.0) × (450/300) = 3.0 × 0.5 × 1.5 = 2.25 L.

Problem 7

A gas at 300 K occupies 2.0 L. Find volume at 450 K with constant pressure and amount. Show the reasoning, not just the conclusion.
Hints

The qualitative direction is an independent check.

Answer and explanation

V₂=2.0×450/300=3.0 L.

Problem 8

Why must 20°C and 40°C not be used directly as a 1:2 temperature ratio?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Absolute temperatures are about 293 K and 313 K; Celsius ratios do not measure proportional thermal energy.

Problem 9

A gauge offset must be restored before using a gas-law ratioA gauge offset must be restored before using a gas-law ratioPressure typeExampleAbsolute valueGauge reading150 kPa above atmosphere250 kPaAtmospheric reference100 kPa100 kPaPabsolute = Pgauge + PatmosphereUse absolute pressure in PV = nRT and pressure ratios.
Original selected pressure-reference example; atmospheric pressure is supplied as 100 kPa rather than asserted as universal.
Interpret the supplied visual. If the gauge reads 150 kPa and the atmosphere is 100 kPa, what pressure enters the ideal-gas equation?
Answer and explanation

250 kPa absolute, the sum of the gauge reading and atmospheric reference.

Absolute pressure is measured relative to vacuum, while gauge pressure is measured relative to the surrounding atmosphere. An ordinary gauge reading of zero therefore does not mean zero molecular collisions or vacuum. In the selected example, a 150 kPa gauge reading with 100 kPa atmosphere corresponds to 250 kPa absolute. Gas-law equations use the absolute pressure; temperature also uses an absolute scale. State both reference conditions rather than treating the printed number on an instrument as automatically suitable.

250 kPa absolute, the sum of the gauge reading and atmospheric reference.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the chemistry relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 10

A fixed ideal-gas amount occupies 3.00 L at 100 kPa absolute and 300 K. Find its volume at 150 kPa and 350 K, and name one model limitation.
Answer and explanation

V₂=3.00(100/150)(350/300)=2.33 L. Assume the same gas amount and ideal behavior; leakage, reaction or condensation would require another account.

V₂=3.00(100/150)(350/300)=2.33 L. Assume the same gas amount and ideal behavior; leakage, reaction or condensation would require another account.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 11

OpenSciEd three-bottle model showing gas particles and motion arrows at room temperature, followed by cooled and warmed bottles with space for the learner to draw particle predictions.
This source diagram has a motion-arrow key and blank cooled/warmed views. It is a learner-prediction template, not measured gas-law data. Gas-bottle model: room temperature, cooling and warming · OpenSciEd · 6.3 Weather, Climate & Water Cycling, Lesson 5, source, CC BY 4.0. Figure excerpt rendered from the PDF and resized for the web.
Complete the source model conceptually for warming a fixed gas amount under a flexible bubble boundary with approximately constant outside pressure. What happens to mean energy, characteristic speed and volume in the ideal model? Contrast a rigid sealed container.
Answer and explanation

Mean translational energy increases with kelvin temperature, characteristic speed for the same species increases with √T, and volume increases proportionally to T under the fixed-pressure ideal model. Keep molecule identity and total count fixed. A rigid sealed vessel fixes volume, so pressure rises instead; blank template regions do not mean zero particles.

Identify the source’s visible labels, scales and unfinished or omitted information.

Use the local complete explanations to connect the observation with an explicit mechanism.

State assumptions and a limit before extending the model.

Response criteria

  • Interpret the source symbols and boundary correctly.
  • Explain the relevant mechanism using quantities/species consistently.
  • State a meaningful omission, assumption or evidence limitation.

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