Carbon in Combustion

Overview

Students investigate combustion as a chemical reaction, model the rearrangement of atoms, and analyse how combustion transfers energy and carbon dioxide between Earth’s spheres. Working in a small team, students use evidence from a safe teacher demonstration to construct and critique representations of the reaction.

Learning intentions

• WALT identify reactants and products in a combustion reaction.
• WALT model how atoms are rearranged and use a balanced equation to show conservation of mass.
• WALT represent energy transfers and explain why combustion is not 100% efficient.
• WALT connect combustion to interactions between the geosphere, biosphere and atmosphere.

Success criteria

• I can identify the fuel and oxygen as reactants and carbon dioxide and water as products.
• I can use particle diagrams and a balanced symbolic equation to show that atoms are conserved.
• I can describe useful and wasted energy outputs and calculate efficiency from supplied data.
• I can explain how burning fossil fuels changes the carbon cycle and atmospheric carbon dioxide.

Curriculum links

• Chemical reactions: modelling the rearrangement of atoms using word and simple balanced chemical equations.
• Carbon cycle: examining combustion and interactions between Earth’s spheres.
• Energy conservation: analysing inputs, outputs, transfers, transformations and efficiency.
• Scientific inquiry and representations: developing explanations and selecting models, tables and diagrams to organise information.

Lesson structure (90 minutes)

1. 0–8 min · Hook and prediction. Teacher displays a photograph of a burning candle beside a sealed jar and asks, “Where do the atoms go when the candle disappears?” using the opening combustion question. Students individually predict what happens to the candle’s matter, then share and record one testable question; the teacher collects contrasting ideas without confirming answers.

2. 8–20 min · Demonstration and evidence. Teacher conducts a safe candle combustion demonstration under a large jar or uses teacher-prepared observations, emphasising that students do not handle flames, and opens the demonstration and observation slides. Students observe the flame, melting wax and water droplets, record qualitative evidence on the combustion investigation worksheet, and discuss whether the system is open or closed.

3. 20–35 min · Direct teaching through modelling. Teacher introduces combustion of methane as a manageable model: methane + oxygen → carbon dioxide + water, then uses particle diagrams to show that carbon, hydrogen and oxygen atoms are rearranged rather than destroyed. Students work in pairs to annotate the model and complete the balanced equation, CH₄ + 2O₂ → CO₂ + 2H₂O, on the combustion investigation worksheet; peers check each element count before the teacher addresses misconceptions.

4. 35–52 min · Collaborative atom challenge. Teacher gives each pair space to construct a reactant-to-product particle model and prompts, “What evidence shows conservation of mass?” using the atom modelling instructions. Students use counters, mini-whiteboards or drawn circles to represent atoms, explain their model to another pair, and revise it after receiving one “agree” and one “question” from their peers.

5. 52–68 min · Energy transfer and efficiency. Teacher presents a simplified combustion energy example: 100 units of chemical energy input, 35 units transferred to useful motion or heating, and 65 units transferred to the surroundings as thermal or sound energy; students view the energy transfer and efficiency slides. Students complete the energy-flow diagram and calculate efficiency using useful output ÷ total input × 100 on the combustion investigation worksheet, then critique why a combustion system cannot be treated as 100% efficient.

6. 68–82 min · Carbon-cycle systems explanation. Teacher displays a four-sphere diagram and asks students to trace carbon before, during and after combustion using the carbon-cycle systems prompt. In a group of five, students create a verbal or drawn explanation linking fossil carbon in the geosphere, combustion in the atmosphere, carbon dioxide uptake by the biosphere through photosynthesis, and respiration; each student must contribute one labelled arrow and one explanation.

7. 82–90 min · Plenary and assessment. Teacher revisits the opening question and displays the final prompts in the plenary and exit questions. Students complete the final section of the combustion investigation worksheet: “Explain why burning methane is a chemical reaction,” “Show how atoms are conserved,” and “Name two spheres involved and describe their interaction”; students submit responses for review.

Resources

• the complete combustion investigation slide deck
• the combustion investigation worksheet
• Teacher demonstration candle, large glass jar and heatproof tray
• Safety glasses and heat-resistant equipment
• Atom counters, coloured paper circles or mini-whiteboards
• Timer and calculator
• Board and markers
• Student science notebooks

Assessment

• Listen for evidence-based predictions, accurate reactant/product identification and peer explanations during modelling.
• Check particle models and equation balances for conservation of each type of atom; question students who treat combustion as matter disappearing.
• Use the final worksheet responses to assess chemical equations, energy efficiency and carbon-cycle sphere interactions.

Differentiation

• Support students with a partially completed particle diagram, an atom-counting table, a word bank, colour-coded carbon/hydrogen/oxygen symbols and sentence starters such as “The reactants are…” and “Carbon moves from… to…”.
• Pair students strategically and assign rotating roles: evidence recorder, model builder, equation checker, energy analyst and spokesperson. Allow oral explanations or labelled diagrams instead of extended writing where appropriate.
• For EAL/D learners, pre-teach “reactant”, “product”, “combustion”, “conserve”, “efficiency” and “sphere” with visuals; accept home-language discussion before students present in English.
• Provide enlarged print, uncluttered worksheet spacing and teacher check-ins for students requiring additional processing time. Extension students balance a second hydrocarbon equation, such as propane combustion, and compare the carbon dioxide produced per unit of chemical energy.

Extension

• Students investigate whether combustion in an open container can appear to lose mass and explain the result by identifying gases leaving the system.
• Students propose one question about reducing combustion emissions and identify the evidence needed to investigate it.