Combustion and Conservation of Mass

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Date:

Part 1: Evidence from Combustion

WALT: identify reactants and products, and use evidence to explain what happens during combustion.

Success criteria: I can identify the fuel and oxygen as reactants; identify carbon dioxide and water as products; and use observations as evidence.

1. Prediction: When a candle appears to disappear, where does its matter go? Explain your prediction using the idea that atoms are not destroyed.

2. Record evidence from the teacher demonstration. Complete each observation and evidence entry.

Observation: flame

Observation: wax

Observation: jar or glass

Evidence that a new substance may form

Evidence of energy transfer

Is the system open or closed? Explain.

3. In methane combustion, name the reactants and products.

Reactants: ________________________________

Products: __________________________________

Part 2: Atoms and Energy

WALT: model the rearrangement of atoms and calculate the efficiency of an energy transfer.

Success criteria: I can count each type of atom on both sides of an equation; show conservation of mass; and calculate efficiency.

4. Complete the methane combustion word equation.

methane + ____________________ → ____________________ + ____________________

5. Use the symbolic equation to answer the atom-counting prompts.

CH₄ + 2O₂ → CO₂ + 2H₂O

Number of carbon atoms: reactants ______ products ______

Number of hydrogen atoms: reactants ______ products ______

Number of oxygen atoms: reactants ______ products ______

How does this equation show conservation of mass?

6. Draw a particle model for CH₄ + 2O₂ → CO₂ + 2H₂O. Use a key for carbon, hydrogen and oxygen atoms.

7. A combustion system receives 100 units of chemical energy. It transfers 35 units to useful motion or heating and 65 units to the surroundings. Calculate its efficiency.

Efficiency = useful output ÷ total input × 100

Efficiency = ____________________ %

Why is the system not 100% efficient?

Part 3: Earth’s Spheres and Explanation

WALT: explain how combustion transfers matter and energy between the geosphere, atmosphere and biosphere.

Success criteria: I can describe a carbon movement between two spheres and explain why burning fossil fuels changes atmospheric carbon dioxide.

8. Explain how carbon can move from the geosphere to the atmosphere during combustion, and how it may later move into the biosphere.

9. Complete the explanation using the word bank and sentence starters.

Word bank: combustion, conserve, carbon dioxide, geosphere, atmosphere, biosphere, reactants, products, energy, efficiency

Sentence starters:

“The reactants are ____________________. The products are ____________________.”

“Atoms are conserved because ____________________.”

“Carbon moves from the ____________________ to the ____________________ when ____________________ occurs.”

10. Challenge: Balance the propane combustion equation and identify the products.

_____C₃H₈ + _____O₂ → _____CO₂ + _____H₂O

Products: __________________________________

Support: Use the word bank, count one element at a time, and label each particle in your model. You may explain your sphere interaction with a labelled diagram or orally before writing.

Extension: Explain why combustion in an open container can appear to lose mass. Identify which gases may leave the system.