Science · Grade 10

Active learning ideas

Balancing Chemical Equations

Active learning works for balancing chemical equations because students often struggle with abstract symbol manipulation. Hands-on counting and modeling make the Law of Conservation of Mass concrete, helping students visualize why only coefficients can change in equations.

• Ontario Curriculum Expectations
• HS-PS1-7

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

Activity 01

• Problem-Based Learning
• 30 min · Pairs

Pairs: Balancing Relay Race

Prepare cards with unbalanced equations. Pairs line up; one student runs to board, balances one equation, tags partner to do next. First pair finishing all correctly wins prizes. Follow with class share-out of strategies used.

Explain the Law of Conservation of Mass in the context of chemical reactions.

Facilitation Tip

In PhET Simulation Practice, ask students to pause and sketch their balanced equations on mini whiteboards before entering values into the tool.

What to look for

Present students with several unbalanced chemical equations. Ask them to identify the number of atoms for each element on both the reactant and product sides for two of the equations. This checks their ability to count atoms accurately.

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

Activity 02

• Problem-Based Learning
• 45 min · Small Groups

Small Groups: Marshmallow Atom Models

Provide colored marshmallows as atoms, toothpicks as bonds. Groups build reactant models from unbalanced equations, then rearrange into products while balancing coefficients. Sketch and label final balanced setup for portfolio.

Construct balanced chemical equations to represent chemical changes.

What to look for

Provide students with a partially balanced equation, missing one or two coefficients. Ask them to determine the missing coefficients and write the final balanced equation. This assesses their skill in applying balancing strategies.

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

Activity 03

• Problem-Based Learning
• 25 min · Whole Class

Whole Class: Coefficient Card Vote

Display unbalanced equation on screen. Students hold number cards (1-4); class votes on coefficients via show of cards, discusses rationale, adjusts to consensus. Repeat for 5-6 equations.

Predict the coefficients needed to balance a given chemical equation.

What to look for

Pose the question: 'Imagine a reaction where you start with 10 grams of reactant A and 5 grams of reactant B, but you only collect 12 grams of product C. What might have happened to the missing 3 grams of mass?' This prompts students to think about the Law of Conservation of Mass and potential experimental errors.

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

Activity 04

• Problem-Based Learning
• 30 min · Individual

Individual: PhET Simulation Practice

Students access Balancing Chemical Equations PhET sim, complete 10 equations with hints off, log strategies in journal. Debrief top challenges as exit ticket.

Explain the Law of Conservation of Mass in the context of chemical reactions.

What to look for

Present students with several unbalanced chemical equations. Ask them to identify the number of atoms for each element on both the reactant and product sides for two of the equations. This checks their ability to count atoms accurately.

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

A few notes on teaching this unit

Teachers should emphasize practice with immediate feedback, as balancing equations requires repetition to build automaticity. Avoid rushing to the algorithm; instead, let students discover patterns through guided discovery. Research shows that peer teaching during activities improves accuracy, so structure opportunities for students to explain their reasoning to each other.

Successful students will confidently count atoms on both sides of equations and adjust coefficients systematically. They will explain why subscripts cannot change and how balancing reflects conservation of mass. Group discussions show they can justify their choices with evidence from models or simulations.

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Watch Out for These Misconceptions

• During Marshmallow Atom Models, watch for students changing the color of marshmallows to represent different atoms instead of keeping colors fixed for each element.

  Remind students that each color represents a specific element (e.g., pink = hydrogen, white = oxygen) and that changing colors would create new substances, which violates the conservation of mass.

• During Balancing Relay Race, watch for students skipping elements or counting molecules instead of individual atoms.

  Ask partners to call out each element one at a time and tally marks on paper to track counts, ensuring they focus on atoms rather than molecules.

• During Coefficient Card Vote, watch for students inventing extra elements not present in the original equation.

  Use the atom inventory table on the board to cross-check each proposed coefficient, ensuring no new elements appear and all original ones are accounted for.

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Methods used in this brief

• Problem-Based Learning