Chemistry · 10th Grade

Active learning ideas

Energy in Chemical Reactions: Exothermic and Endothermic

Active learning works for this topic because students’ physical experience of heat or cold in chemical reactions creates lasting neural pathways. When students feel a temperature change during a hands-on demo, the surprise of cold from a reaction they associate with ‘heat’ anchors the concept more firmly than a lecture ever could.

• Common Core State Standards
• STD.HS-PS1-4
• STD.HS-PS3-1

• 20–35 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Experiential Learning
• 30 min · Small Groups

Predict-Observe-Explain: Hot and Cold Pack Demos

Students predict whether dissolving calcium chloride and dissolving ammonium nitrate in water will feel warm or cold. After observing temperature changes with thermometers, they use bond energy reasoning to explain why each behaves as it does, identifying which process (bond breaking or bond forming) dominates in each case.

Explain where the energy goes when a reaction feels cold.

Facilitation Tip

During the Hot and Cold Pack Demos, circulate with an infrared thermometer to let students see real-time temperature changes projected on a screen.

What to look for

Provide students with a list of common chemical processes (e.g., burning wood, ice melting, cellular respiration, photosynthesis). Ask them to label each as exothermic or endothermic and provide a one-sentence justification based on whether heat is released or absorbed.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 02

• Think-Pair-Share
• 20 min · Pairs

Think-Pair-Share: Where Does the Energy Go?

Ask students where the energy goes during an endothermic reaction if it seems to 'disappear.' Students write individual responses connecting energy conservation to the formation of higher-energy bonds in the products. Pairs compare and then contribute to a class-level energy balance diagram on the board.

Differentiate between exothermic and endothermic reactions.

Facilitation Tip

In the Think-Pair-Share on energy flow, provide energy accounting diagrams as sentence frames so students practice translating observations into energy notation.

What to look for

Present students with a scenario: 'A reaction mixture feels cold to the touch.' Ask them to: 1. Classify the reaction as exothermic or endothermic. 2. Explain what is happening to the energy at the molecular level, referencing bond breaking and forming.

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

Activity 03

• Gallery Walk
• 35 min · Small Groups

Gallery Walk: Exothermic and Endothermic in Daily Life

Six stations each show a real-world process: combustion of natural gas, photosynthesis, dissolving NaOH, ice packs, hand warmers, and respiration. Students classify each as exothermic or endothermic and write a one-sentence justification using bond energy language. Groups compare classifications and debate any disagreements.

Analyze how bond breaking and forming contribute to enthalpy changes.

Facilitation Tip

For the Gallery Walk, assign each poster a unique real-world example so students connect the energy concept to diverse contexts beyond the classroom.

What to look for

Pose the question: 'If breaking bonds always requires energy and forming bonds always releases energy, how can we predict if a reaction will be exothermic or endothermic?' Facilitate a class discussion focusing on the net energy change resulting from the balance between bond breaking and bond forming.

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

A few notes on teaching this unit

Start with the Hot and Cold Pack Demos to create cognitive conflict, then use the Think-Pair-Share to formalize the vocabulary of exothermic and endothermic. Avoid rushing to the definitions before students experience the phenomena; research shows this delay strengthens long-term retention. Always connect back to bond energy diagrams to prevent students from reducing the topic to simple memorization of examples.

Successful learning looks like students confidently classifying reactions, tracing energy flow with diagrams, and applying the concepts to new contexts without mixing up exothermic and endothermic labels. You will see students using the language of bond energy and thermal energy interchangeably as they explain their reasoning.

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Watch Out for These Misconceptions

• During the Hot and Cold Pack Demos, watch for students who assume all reactions release heat because they have only experienced burning or explosions.

  After the cold-pack demonstration, have students draw energy flow diagrams showing reactants’ bond energy converting to thermal energy of the surroundings in the exothermic case and thermal energy of the surroundings converting to products’ bond energy in the endothermic case.

• During the Think-Pair-Share on energy flow, watch for students who believe energy is created or destroyed during exothermic reactions.

  Use the energy accounting sheets from the Think-Pair-Share to explicitly calculate total energy before and after the reaction, labeling bond energies and thermal energy to reinforce the Law of Conservation of Energy.

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Methods used in this brief

• Experiential Learning
• Think-Pair-Share
• Gallery Walk