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Balancing Chemical Equations

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Balancing Chemical Equations

Balance each equation by changing coefficients only. Use the smallest whole-number coefficients, and show your reasoning where asked. A coefficient of 1 may be written as 1 or left blank.

The reaction audit

At a materials-recovery plant, chemists check reaction equations to make sure every atom is accounted for. The atom-count grid is provided for Question 2.

1.A student says, “Balancing an equation creates extra atoms on one side.” Which principle explains why this is incorrect?

The law of conservation of mass: atoms are rearranged, not created or destroyed.
The law of definite proportions: every compound has a fixed composition.
The idea that reactions always release energy.
The rule that all reactions produce a gas.

Element

Reactants

Products

Hydrogen (H)

4 atoms

Oxygen (O)

2 atoms

2.Use the atom-count audit above. Is 2H₂ + O₂ → 2H₂O balanced? State the total number of each type of atom on both sides.

3.In a hydrocarbon combustion equation, carbon and hydrogen are usually balanced before oxygen. Why is oxygen commonly balanced last?

Balance the reaction records

Place coefficients in front of formulae. Do not alter subscripts: a changed subscript would describe a different substance.

4.Balance methane combustion: CH₄ + O₂ → CO₂ + H₂O. Write the complete equation with the smallest whole-number coefficients.

5.Balance this neutralisation reaction: HCl + NaOH → NaCl + H₂O. Include coefficients, even if some are 1.

6.Balance ethane combustion: C₂H₆ + O₂ → CO₂ + H₂O. Use the smallest whole-number coefficients.

7.Balance propane combustion: C₃H₈ + O₂ → CO₂ + H₂O. Check that your final coefficients are in the simplest whole-number ratio.

8.A classmate changes H₂O to H₂O₂ to make an oxygen count work. Explain why this is not a valid balancing step, and state what should be changed instead.

9.A methane burner has limited oxygen, so methane undergoes incomplete combustion and forms carbon monoxide and water: CH₄ + O₂ → CO + H₂O. Balance this equation using the smallest whole-number coefficients.

10.Explain how you can verify that your answer to Question 9 is balanced. Give the atom totals on each side for carbon, hydrogen and oxygen.

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For Teachers & Parents

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