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F. Gases and Atmospheric Chemistry · Gases and Atmospheric Chemistry

Gases and Atmospheric Chemistry: Unit Review

F1.1 F1.2 F2.1 F2.2 F2.3 F2.4 F2.5 F3.1 F3.2 F3.3 F3.4 F3.5 F3.6 A1.1 A1.4 A1.5 A1.6 A1.8 A1.9 A1.10 A1.12 A1.13 A2.1About 40 minutes
Learning goals
  • I can explain gas behaviour with intermolecular forces and the kinetic molecular theory.
  • I can solve problems with the gas laws, the ideal gas law, Dalton's law and gas stoichiometry.
  • I can plan, analyse and evaluate gas investigations.
  • I can describe the atmosphere, air pollutants and their sources, and evaluate ways to improve air quality.

Words to know

ideal gas law
PV = nRT, with R = 8.314 kPa·L/(mol·K).
combined gas law
P₁V₁/T₁ = P₂V₂/T₂ for a fixed amount of gas.
molar volume
22.4 L/mol at STP; 24.8 L/mol at SATP.
partial pressure
The pressure one gas in a mixture would exert alone; P(A) = x(A) × P(total).
AQHI
Air Quality Health Index: 1 to 10+, based on O₃, PM2.5 and NO₂.

Let's review!

In this unit you explained the states of matter with intermolecular forces and described gases with the kinetic molecular theory. You measured pressure and temperature correctly, then learned Boyle's, Charles's, Gay-Lussac's and the combined gas laws, tested them with investigations, and met Avogadro's hypothesis, molar volume, the ideal gas law and Dalton's law of partial pressures. You used them for gas stoichiometry and to find a gas's molar volume and molar mass by experiment. Finally you studied the atmosphere, how human activities and technologies affect air quality, your carbon footprint, and Canadian initiatives to clean the air.

This review has a few questions from every lesson. Try each one, then press Show answer to check.

How to use this review

Do one or two sections at a time. For every calculation: list the givens with units, convert temperatures to kelvins, match pressure and volume units, predict whether the answer should be bigger or smaller, and only then calculate. Round final answers to the right number of significant figures. For every question you get wrong, write down why (wrong law? forgot K? forgot water vapour? skipped the mole ratio?) and reread that lesson's worked examples. Finish with the 10-question quiz.

BoyleP₁V₁ = P₂V₂T, n constantCharlesV₁/T₁ = V₂/T₂P, n constantGay-LussacP₁/T₁ = P₂/T₂V, n constantCombinedP₁V₁/T₁ = P₂V₂/T₂n constantAvogadroV₁/n₁ = V₂/n₂; Vₘ22.4 (STP), 24.8 (SATP) L/molIdeal gasPV = nRTR = 8.314 kPa·L/(mol·K)DaltonP(total) = P₁ + P₂ + ...P(A) = x(A) × P(total)Always: temperature in K, matching units, predict before you calculate
Summary of the gas laws in this unit. The combined gas law contains Boyle's, Charles's and Gay-Lussac's laws; the ideal gas law adds the amount of gas.
Clean dry airN₂ 78 %, O₂ 21 %Ar 0.93 %, CO₂ ≈ 420 ppmPrimary pollutantsCO, NOx, SO₂, VOCs, PMvehicles, smelters, firesSecondary pollutantsground-level O₃ (smog)H₂SO₄, HNO₃ (acid)Solutionsmeasure (AQHI), reduce at the source (catalytic converters,SO₂ capture, coal phase-out, burning less fuel), evaluate with evidence
Summary of atmospheric chemistry: what clean air contains, where pollutants come from, how secondary pollutants form, and how we respond.

States of Matter and Intermolecular Forces

1

Rank from lowest to highest boiling point and explain: H₂O, CH₄, H₂S.

2

Snow slowly disappears on a cold, sunny day without melting. Name the change and say whether it absorbs or releases energy.

3

What is the only intermolecular force between Cl₂ molecules?

The Kinetic Molecular Theory and Ideal Gases

1

Which two KMT postulates best explain why gases are compressible and fill their containers?

2

At the same temperature, which atoms move faster on average, Ne or Kr? Why?

3

Under what conditions do real gases deviate most from ideal behaviour?

Measuring Gases: Pressure, Temperature, STP and SATP

1

Convert 95.0 kPa to atm and to mmHg.

2

Convert −15 °C to kelvins.

3

A tire gauge reads 180 kPa when air pressure is 101 kPa. What is the absolute pressure?

Boyle's Law: Pressure and Volume

1

A 3.0 L gas sample at 120 kPa is compressed to 2.0 L at constant temperature. Find the new pressure.

2

What graph gives a straight line through the origin for Boyle's law?

3

Explain Boyle's law with the KMT.

Charles's Law: Volume, Temperature and Absolute Zero

1

A 1.0 L balloon at 20 °C is warmed to 80 °C at constant pressure. Find its new volume.

2

How did V–t graphs lead to the idea of absolute zero?

3

Why does heating a gas from 10 °C to 20 °C not double its volume?

Gay-Lussac's Law and the Combined Gas Law

1

A rigid can holds gas at 200 kPa and 25 °C. Find the pressure at 50 °C.

2

4.0 L of gas at 101 kPa and 20 °C changes to 80 kPa and −20 °C. Find the new volume.

3

Which variable is held constant in Gay-Lussac's law?

Investigating Gas Laws: Planning, Data and Error

1

In an investigation of how temperature affects gas pressure, name the independent, dependent and controlled variables.

2

An experimental absolute zero is −268 °C. Find the percentage error.

3

A syringe leaks during a Boyle's law experiment. How does this affect the values of P × V?

Avogadro's Hypothesis and Molar Volume

1

State Avogadro's hypothesis.

2

What volume does 6.4 g of SO₂ occupy at SATP?

3

For 2 CO(g) + O₂(g) → 2 CO₂(g), what volume of O₂ reacts with 8.0 L of CO (same T and P)?

The Ideal Gas Law: PV = nRT

1

Find the pressure of 0.300 mol of gas in a 1.50 L flask at 25 °C.

2

0.85 g of a noble gas occupies 250 mL at 25 °C and 101.3 kPa. Find its molar mass and identify it.

3

When should you use PV = nRT instead of the combined gas law?

Just for fun

A gas-law limerick:

A gas in a can, feeling hot, Said, "My pressure is climbing a lot!" Gay-Lussac replied, "With your volume tied, Your kelvins decide what you've got."

Dalton's Law of Partial Pressures

1

Hydrogen is collected over water at 22 °C and 100.0 kPa. What is the pressure of the dry hydrogen?

2

A gas mixture at 250 kPa is 20 % CO₂ by moles. Find P(CO₂).

3

Why is breathing harder at high altitude even though the air is still about 21 % oxygen?

Gas Stoichiometry

1

What volume of H₂ at 22 °C and 100 kPa is made when 2.43 g of Mg reacts with excess HCl? Mg + 2 HCl → MgCl₂ + H₂

2

For CH₄ + 2 O₂ → CO₂ + 2 H₂O, what volume of O₂ burns 3.0 L of CH₄ (same T and P)?

3

Why does every stoichiometry route pass through moles?

Inquiry: Finding the Molar Volume and Molar Mass of a Gas

1

Why is Mg ribbon cleaned before an experiment to find molar volume?

2

A student forgets to subtract water vapour pressure. Is her molar volume too high or too low?

3

Which WHMIS hazards apply to hydrochloric acid and to hydrogen gas?

The Atmosphere: Composition, Layers and Pollutants

1

Give the approximate percentages of N₂, O₂ and Ar in dry air, and the concentration of CO₂ in ppm.

2

Is ground-level ozone a primary or a secondary pollutant? Explain.

3

Write the equation for the formation of NO in a car engine.

Human Activities, Technology and Air Quality: Your Carbon Footprint

1

About how much CO₂ comes from burning 40 L of gasoline?

2

Why doesn't a catalytic converter lower CO₂ emissions?

3

Why didn't the Superstack solve Sudbury's SO₂ problem?

Assessing Air Quality and Canadian Initiatives

1

An AQHI of 4 is in which risk category?

2

Name two Canadian initiatives that reduced acid rain or smog.

3

Give two questions you should ask when evaluating an air quality initiative.

Check your understanding

Quiz

1.

Which intermolecular force explains why water has a much higher boiling point than H₂S?

2.

According to the KMT, the average kinetic energy of a gas depends only on its:

3.

A gas at 100 kPa occupies 6.0 L. At constant temperature, its volume at 150 kPa is:

4.

A gas at 300 K is heated to 600 K in a rigid container. Its pressure:

5.

What volume does 0.250 mol of gas occupy at STP?

6.

Using PV = nRT, how many moles are in 24.9 L of gas at 300 K and 100 kPa?

7.

Oxygen is collected over water at 25 °C (water vapour pressure 3.17 kPa) and 101.3 kPa. P(O₂) is:

8.

For N₂ + 3 H₂ → 2 NH₃, 9.0 L of H₂ (same T and P) produces:

9.

Which is a secondary pollutant?

10.

The AQHI is based on the health risk from:

For parents and teachers

How to use the results: each section of the review matches one lesson. If your teen misses a question, go back to that lesson's worked examples.

  • Boiling points, states, phase changes: States of Matter and Intermolecular Forces.
  • Explaining gas behaviour in words: The Kinetic Molecular Theory and Ideal Gases.
  • Unit conversions, forgetting kelvins, gauge pressure: Measuring Gases.
  • P–V, V–T and P–T problems wrong (often a rearranging error): the Boyle's Law, Charles's Law and Gay-Lussac's Law and the Combined Gas Law lessons. Check that the answer matches a prediction.
  • Variables, percentage error, error direction: Investigating Gas Laws and Inquiry: Finding the Molar Volume and Molar Mass of a Gas.
  • Using 22.4 or 24.8 L/mol at the wrong conditions: Avogadro's Hypothesis and Molar Volume; use PV = nRT otherwise (The Ideal Gas Law).
  • Forgetting water vapour, partial pressure errors: Dalton's Law of Partial Pressures.
  • Skipping the mole ratio: Gas Stoichiometry (and the unit Quantities in Chemical Reactions).
  • Pollutants, sources, equations: The Atmosphere.
  • Carbon footprint calculations and proposals: Human Activities, Technology and Air Quality.
  • AQHI and evaluating initiatives: Assessing Air Quality and Canadian Initiatives.

Looking ahead: the gas laws return in Grade 12 Chemistry (SCH4U) in energy changes, reaction rates and equilibrium, and in Grade 12 Physics. The air quality and carbon footprint skills connect to Grade 12 environmental science and to everyday citizenship.