Chemistry · Grade 11

Active learning ideas

Real Gases vs. Ideal Gases

Active learning works exceptionally well for real versus ideal gases because students often struggle to visualize the invisible forces at play. Engaging with simulations and data lets them see deviations as dynamic, measurable phenomena rather than abstract concepts. This hands-on approach builds intuition for why real gases behave differently under specific conditions.

• Ontario Curriculum Expectations
• HS-PS1-3

• 25–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Simulation Game
• 35 min · Pairs

PhET Simulation: Real Gas Deviations

Direct pairs to the PhET Gas Properties simulation set to real gas mode. Have them adjust pressure from 1 to 100 atm and temperature from 100 K to 500 K, recording Z values in a table. Pairs then graph Z vs P and identify conditions of largest deviation.

Explain the molecular reasons why real gases deviate from ideal gas behavior at high pressures and low temperatures.

Facilitation Tip

In the PhET simulation, have students toggle the 'intermolecular forces' and 'particle size' sliders separately to isolate their effects on gas behavior.

What to look for

Present students with a graph showing the compressibility factor (Z) versus pressure for several gases at a constant low temperature. Ask: 'Which gas shows the most deviation from ideal behavior at high pressures? Explain your reasoning based on intermolecular forces and particle volume.'

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 02

• Simulation Game
• 45 min · Small Groups

Graphing Stations: Compressibility Curves

Prepare stations with data for CO2, N2, and He at varying P and T. Small groups plot Z vs P graphs at fixed T, rotating stations. Conclude with whole-class share-out on trends.

Compare the behavior of an ideal gas to that of a real gas under extreme conditions.

Facilitation Tip

At the graphing stations, provide a blank template of the compressibility factor (Z) versus pressure curve for students to sketch predictions before analyzing data.

What to look for

Pose the following scenario: 'Imagine a gas cylinder containing helium at room temperature and atmospheric pressure, and another cylinder containing ammonia under high pressure and low temperature. Which gas is more likely to deviate significantly from ideal gas behavior? Justify your answer by discussing the specific properties of each gas.'

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 03

• Simulation Game
• 30 min · Pairs

Van der Waals Calculations: Pairs Challenge

Provide van der Waals constants a and b for several gases. Pairs calculate corrected P and V for given conditions, compare to ideal values, and predict which gas deviates most under high P low T.

Predict how the intermolecular forces and particle volume of a real gas affect its pressure and volume compared to an ideal gas.

Facilitation Tip

During the van der Waals pairs challenge, circulate to listen for students explaining how 'a' and 'b' terms account for attractions and volume in their calculations.

What to look for

Ask students to write two sentences explaining why real gases behave differently from ideal gases at high pressures, and two sentences explaining why they behave differently at low temperatures. They should use at least two key vocabulary terms in their answers.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 04

• Simulation Game
• 25 min · Whole Class

Demo Discussion: Dry Ice Pressure

Demonstrate pressure buildup from dry ice in a sealed flask at room T vs cooled. Students predict ideal vs real behavior beforehand, then explain observations in whole class using molecular terms.

Explain the molecular reasons why real gases deviate from ideal gas behavior at high pressures and low temperatures.

Facilitation Tip

For the dry ice demo, ask students to predict gas behavior before pressure changes occur, then revisit their answers after observing the results.

What to look for

Present students with a graph showing the compressibility factor (Z) versus pressure for several gases at a constant low temperature. Ask: 'Which gas shows the most deviation from ideal behavior at high pressures? Explain your reasoning based on intermolecular forces and particle volume.'

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

A few notes on teaching this unit

Teachers should emphasize that real gases are the norm, while ideal gases are a simplified model used for convenience. Avoid presenting deviations as exceptions to an ideal rule—instead, frame them as natural consequences of molecular dynamics. Research shows students grasp intermolecular forces better when they see how temperature and pressure alter particle motion directly. Use analogies cautiously; instead, rely on simulations and data to build evidence-based reasoning.

By the end of these activities, students will confidently explain why real gases deviate from ideal behavior under high pressures and low temperatures. They will analyze graphs, apply the van der Waals equation, and justify their reasoning using precise vocabulary and data. Success looks like students connecting molecular behavior to macroscopic observations and adjusting their model predictions accordingly.

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Watch Out for These Misconceptions

• During the PhET Simulation: Real Gas Deviations, watch for students assuming deviations occur under all conditions.

  During the PhET simulation, guide students to adjust pressure and temperature sliders to observe where Z approaches 1, reinforcing that ideal behavior is the exception at low pressures and high temperatures.

• During the Graphing Stations: Compressibility Curves, watch for students attributing pressure decreases to particle volume.

  During graphing stations, have students compare Z values above and below 1, and ask them to trace how crowding at high pressures leads to higher-than-ideal pressure readings.

• During the Demo Discussion: Dry Ice Pressure, watch for students claiming intermolecular forces increase pressure.

  During the dry ice demo, have students compare the behavior of cooled and heated gases, noting how reduced particle speed at low temperatures enhances attractions and lowers pressure.

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Methods used in this brief

• Simulation Game