Bond Breaking and Bond Making

Active learning works for bond breaking and bond making because students often confuse energy changes with the idea of energy being ‘used up’ or ‘created.’ Hands-on modeling and real-time measurements help them directly experience the energy costs of breaking bonds and the energy rewards of making them.

• Year 10
• Chemistry
• 4 activities
• 25 min–40 min

Learning Objectives

1. Explain why energy input is required to break chemical bonds, identifying this as an endothermic process.
2. Explain why energy is released when new chemical bonds are formed, identifying this as an exothermic process.
3. Calculate the overall energy change of a reaction by comparing the energy required to break reactant bonds with the energy released during product bond formation.
4. Differentiate between endothermic and exothermic reactions based on the relative energy changes of bond breaking and bond making.

Think-Pair-Share

⏱ 30 min·Small Groups

Modeling: Rubber Band Bonds

Provide rubber bands as bonds between paper atoms. Students stretch bands to break bonds, noting effort required, then snap new ones, observing energy release as vibration. Groups record qualitative energy observations and discuss endothermic versus exothermic steps.

Prepare & details

Explain why bond breaking is an endothermic process.

Facilitation Tip: For the Rubber Band Bonds activity, walk pairs through stretching the band slowly to feel the increasing resistance before it snaps, linking this physical effort to energy absorption during bond breaking.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

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

Think-Pair-Share

⏱ 40 min·Pairs

Demo Analysis: Salt Dissolutions

Demonstrate dissolving ammonium nitrate in water (endothermic, cools) and calcium chloride (exothermic, warms). Students in pairs measure temperature changes with thermometers, link to bond disruptions in ionic lattices, and sketch simple energy diagrams.

Prepare & details

Explain why bond making is an exothermic process.

Facilitation Tip: During the Salt Dissolutions demo, have students record temperature changes every 10 seconds for two minutes to capture the full exothermic or endothermic trend.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

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

Think-Pair-Share

⏱ 35 min·Small Groups

Card Sort: Bond Energies

Prepare cards with bond types, energies, and process labels. Small groups sort into endothermic (breaking) or exothermic (making) piles, then calculate net energy for sample reactions using provided values. Pairs present one calculation to class.

Prepare & details

Differentiate between the energy changes associated with breaking and forming chemical bonds.

Facilitation Tip: In the Card Sort activity, ask students to verbalize their reasoning for each bond energy pair before revealing the answer to surface hidden assumptions.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

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

Think-Pair-Share

⏱ 25 min·Individual

Diagram Construction: Reaction Profiles

Individuals draw energy level diagrams for given reactions, labelling bond breaking uphill and making downhill. Share in pairs for peer feedback, then whole class compares endo/exothermic profiles on board.

Prepare & details

Explain why bond breaking is an endothermic process.

Facilitation Tip: For Reaction Profiles, insist students label the activation energy peak before calculating the overall energy change to prevent skipping the critical energy barrier step.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

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

Teaching This Topic

Teachers should anchor energy concepts in concrete, observable changes rather than abstract rules. Avoid starting with definitions; instead, let students gather evidence first, then build the definitions from their observations. Research shows that students grasp bond energy calculations better when they connect bond strengths to real temperature changes they can measure, rather than memorizing tables alone.

What to Expect

Successful learning looks like students consistently linking bond changes to energy transfers, using quantitative data to explain why reactions feel hot or cold, and correcting common misconceptions through evidence from their own experiments and models.

Watch Out for These Misconceptions

Common Misconception

During Rubber Band Bonds, watch for students saying the band ‘releases energy’ as it snaps, as if energy is created.

What to Teach Instead

Pause the activity and ask each pair to count how many times they must stretch the band before it breaks, then connect the number of stretches to total energy absorbed before the release.

Common Misconception

During Salt Dissolutions, watch for students attributing temperature changes to the salt itself rather than bond interactions in solution.

What to Teach Instead

Have pairs share their temperature graphs aloud and ask the class to identify where energy is absorbed or released at the particle level, using the demo setup as evidence.

Common Misconception

During Card Sort: Bond Energies, watch for students assuming all bond formations require energy because they see positive values on cards.

What to Teach Instead

Prompt groups to sort cards into two piles—energy absorbed and energy released—and then discuss why the sign convention matches the physical process.

Assessment Ideas

Quick Check

After Rubber Band Bonds, present a simple reaction diagram and ask students to label which bonds are breaking and forming, and to circle whether energy is absorbed or released at each stage, using their model as a reference.

Exit Ticket

After Card Sort: Bond Energies, provide the statement: ‘In the reaction between hydrogen and chlorine to form hydrogen chloride, more energy is released than absorbed.’ Ask students to explain why this indicates an exothermic reaction, referencing the bond energy values they sorted.

Discussion Prompt

After Salt Dissolutions, pose the question: ‘Why does lighting a match feel hot, but melting ice requires energy input?’ Guide students to discuss the bond breaking and making involved in each process using their temperature data and the demo as evidence.

Extensions & Scaffolding

• Challenge students who finish early to design a mini-experiment testing how particle size affects the temperature change in salt dissolution, guiding them to control variables and justify their method.
• For students who struggle, provide pre-calculated bond energy values on the Card Sort cards so they can focus on the comparison step without being overwhelmed by arithmetic.
• Deeper exploration: Ask students to research a real-world application like cold packs for sports injuries or hand warmers, then present how bond breaking and making control the temperature change in each product.

Key Vocabulary

Endothermic Process	A process that absorbs energy from its surroundings. In chemical reactions, this energy is used to break existing bonds.
Exothermic Process	A process that releases energy into its surroundings. In chemical reactions, this energy is released when new bonds are formed.
Bond Breaking	The process of separating atoms that are joined by chemical bonds. This requires an input of energy.
Bond Making	The process of atoms joining together to form chemical bonds. This releases energy.
Energy Change	The difference between the energy required to break bonds in reactants and the energy released when bonds are formed in products, determining if a reaction is endothermic or exothermic overall.