Chemistry · 12th Grade

Active learning ideas

Entropy and Spontaneity

Active learning works for entropy and spontaneity because students need to confront their intuitive misconceptions directly. Hands-on sorting, discussion, and calculation tasks force them to notice contradictions between their beliefs and observed phenomena, making abstract thermodynamic concepts concrete.

• Common Core State Standards
• HS-PS3-1
• HS-PS3-4

• 25–40 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Inquiry Circle
• 40 min · Small Groups

Inquiry Circle: Spontaneous or Not?

Groups receive eight process cards , dissolving sugar, melting ice at 25 degrees Celsius, burning wood, rusting iron, water freezing at minus 10 degrees Celsius, and similar examples , and sort them into spontaneous versus non-spontaneous based on their initial understanding. After the sort, groups estimate or calculate H and S for each process and revise their sort. The class debrief focuses on cases where groups disagreed or were surprised.

Justify why do some endothermic reactions occur spontaneously?

Facilitation Tip

During Collaborative Investigation: Spontaneous or Not?, circulate and listen for students using ‘speed’ language about spontaneity, then immediately prompt them to justify their choices with energy and disorder reasoning.

What to look for

Present students with 3-4 chemical reactions, each with given $\Delta H$ and $\Delta S$ values. Ask them to calculate $\Delta G$ at 25°C and classify each reaction as spontaneous or non-spontaneous under these conditions.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Think-Pair-Share
• 25 min · Pairs

Think-Pair-Share: The Endothermic Surprise

Present a demonstration or video of ammonium nitrate dissolving in water , a clearly endothermic and spontaneous process. Ask students: if this reaction absorbs heat, why does it happen on its own? Students reason individually using S as a guiding concept, then discuss with a partner. The class builds a shared explanation for entropy-driven spontaneity that goes beyond the naive energy argument.

Explain how does the universe move toward a state of higher entropy?

Facilitation Tip

For Think-Pair-Share: The Endothermic Surprise, ensure pairs include at least one example where ΔS is positive and ΔH is positive to push beyond their initial exothermic bias.

What to look for

Pose the question: 'Why can some endothermic reactions, like ice melting on a warm day, occur spontaneously?' Facilitate a class discussion where students connect this phenomenon to the increase in entropy and the role of temperature in the Gibbs free energy equation.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 03

• Gallery Walk
• 30 min · Small Groups

Gallery Walk: H and S Combinations

Post four stations, each representing one combination of H and S signs: negative/positive, positive/negative, negative/negative, and positive/positive. Students must provide a real chemical example for their station's combination, explain when and whether it is spontaneous, and connect their reasoning to the G = H - TS equation. Groups rotate and build on previous groups' examples and corrections.

Analyze what balance between enthalpy and entropy determines if a process is thermodynamically favored?

Facilitation Tip

In Gallery Walk: H and S Combinations, place a mix of familiar and unfamiliar processes on walls so students practice applying ΔG = ΔH − TΔS across contexts.

What to look for

Provide students with a scenario: 'Consider the process of water evaporating at room temperature.' Ask them to write one sentence explaining the sign of $\Delta H$ and $\Delta S$ for this process, and one sentence explaining why it is spontaneous.

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

A few notes on teaching this unit

Teach this topic by starting with observable, everyday processes students think they understand, then systematically dismantle their assumptions. Avoid leading with equations; instead, let students experience confusion first, then guide them to find the equations as tools to resolve that confusion. Research shows students grasp spontaneity better when they first confront the limits of their ‘fast = spontaneous’ intuition before seeing the math.

Successful learning looks like students correctly relating entropy, enthalpy, and spontaneity without conflating speed with spontaneity or excluding endothermic processes. They should explain why a process is or isn’t spontaneous using ΔG = ΔH − TΔS and connect this to entropy changes in the universe.

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Watch Out for These Misconceptions

• During Collaborative Investigation: Spontaneous or Not?, watch for students labeling slow processes like diamond graphitizing as non-spontaneous.

  During Collaborative Investigation: Spontaneous or Not?, redirect by asking: ‘Does the process favor the products energetically, even if it takes a long time?’ Have them add a column to their chart labeled ‘Speed vs. Spontaneity’ to separate the concepts.

• During Think-Pair-Share: The Endothermic Surprise, expect students to argue that endothermic processes cannot be spontaneous.

  During Think-Pair-Share: The Endothermic Surprise, ask pairs to calculate ΔG for an endothermic spontaneous process at high temperature using the Gibbs equation from their notes, then explain how entropy change outweighs enthalpy change.

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Methods used in this brief

• Inquiry Circle
• Think-Pair-Share
• Gallery Walk