Chemistry · Grade 12

Active learning ideas

Gibbs Free Energy & Equilibrium

This topic demands students connect abstract equations to observable phenomena, which active learning makes possible. Calculations of ΔG and its temperature dependence hide the physical meaning until students manipulate variables and see outcomes in real or simulated reactions. Hands-on work turns abstract signs and symbols into tangible understanding of spontaneity and equilibrium.

• Ontario Curriculum Expectations
• HS-PS1-4

• 25–50 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Problem-Based Learning
• 35 min · Pairs

Pairs Calculation: Temperature Effects on ΔG

Provide pairs with ΔH and ΔS values for five reactions. They calculate ΔG at 298 K, 500 K, and 1000 K, then determine spontaneity at each. Pairs graph ΔG vs. T and predict equilibrium shifts.

Calculate Gibbs free energy change for a reaction and predict its spontaneity.

Facilitation Tip

During the Pairs Calculation, circulate to check that students use consistent units (kJ vs J) when combining ΔH and TΔS.

What to look for

Present students with three reaction scenarios, each with given ΔH, ΔS, and T values. Ask them to calculate ΔG for each and state whether the reaction is spontaneous, non-spontaneous, or at equilibrium. For example: Scenario 1: ΔH = -50 kJ/mol, ΔS = +100 J/mol·K, T = 300 K.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Activity 02

• Problem-Based Learning
• 45 min · Small Groups

Small Groups Demo: Cobalt Complex Equilibrium

Groups heat and cool cobalt chloride solutions to observe color shifts in [Co(H2O)6]2+ ⇌ [CoCl4]2-. They measure approximate ΔH from temperature data, calculate ΔG, and explain shifts using ΔS considerations.

Explain the relationship between Gibbs free energy, enthalpy, and entropy.

Facilitation Tip

In the Small Groups Demo, ask groups to predict the color change direction before adding heat or cold, then compare predictions to observations.

What to look for

Pose the question: 'How can a reaction that is non-spontaneous at room temperature become spontaneous at a higher temperature?' Guide students to discuss the roles of ΔH and ΔS in the ΔG = ΔH - TΔS equation and how temperature's influence changes the sign of the TΔS term.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Activity 03

• Problem-Based Learning
• 50 min · Whole Class

Whole Class Simulation: Reaction Coordinate Explorer

Project PhET or ChemCollective simulation. Class votes on spontaneity predictions before varying T, ΔH, ΔS. Debrief connects observations to ΔG equation and K values.

Analyze how temperature influences the spontaneity of a reaction and its equilibrium position.

Facilitation Tip

While running the Whole Class Simulation, pause at key points to have students predict whether ΔG will become positive or negative as temperature increases.

What to look for

Provide students with a value for K (e.g., K = 1.5 x 10^5). Ask them to calculate the corresponding ΔG° at 298 K (using R = 8.314 J/mol·K) and interpret what the K value and their calculated ΔG° tell them about the reaction's equilibrium position and spontaneity.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Activity 04

• Problem-Based Learning
• 25 min · Individual

Individual Worksheet: ΔG and K Connection

Students use tables to compute ΔG° for reactions, then find K from ΔG° = -RT ln K. They classify K magnitudes and predict Q vs. K direction.

Calculate Gibbs free energy change for a reaction and predict its spontaneity.

Facilitation Tip

For the Individual Worksheet, provide a reference table of R values and remind students to convert ln K to ΔG° using the correct sign.

What to look for

Present students with three reaction scenarios, each with given ΔH, ΔS, and T values. Ask them to calculate ΔG for each and state whether the reaction is spontaneous, non-spontaneous, or at equilibrium. For example: Scenario 1: ΔH = -50 kJ/mol, ΔS = +100 J/mol·K, T = 300 K.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

A few notes on teaching this unit

Teach Gibbs free energy by anchoring discussions in kinetic barriers and real reactions students can visualize. Avoid teaching ΔG as just another formula to memorize. Use temperature as a lever to show how spontaneity flips, and emphasize that equilibrium is a dynamic balance, not a static endpoint. Research shows students grasp entropy better when they see it in action, so include entropy-changing demonstrations before formal definitions.

Successful learning shows when students correctly calculate ΔG for different temperatures, explain why a reaction’s spontaneity can reverse with temperature, and relate equilibrium constants to ΔG°. They should articulate how ΔH and ΔS interact under changing conditions and use ΔG° = -RT ln K to predict reaction direction from K values.

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Watch Out for These Misconceptions

• During the Pairs Calculation: Temperature Effects on ΔG, watch for students assuming reactions with negative ΔG always occur rapidly.

  During the Pairs Calculation, include a short reflection question asking students to compare diamond to graphite transformation (spontaneous but slow) with an explosive reaction (fast but not necessarily spontaneous), using their calculated ΔG signs to justify their reasoning.

• During the Small Groups Demo: Cobalt Complex Equilibrium, watch for students equating exothermic with always spontaneous.

  During the Small Groups Demo, have students measure temperature changes and solubility data, then ask them to explain how an endothermic process can still be spontaneous by examining the TΔS term in their ΔG calculations.

• During the Whole Class Simulation: Reaction Coordinate Explorer, watch for students thinking ΔG is always zero at equilibrium regardless of temperature.

  During the Whole Class Simulation, pause the simulation at different temperatures and ask students to calculate ΔG for the system at each point, reinforcing that ΔG = 0 only at equilibrium for that specific temperature.

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Methods used in this brief

• Problem-Based Learning