Balancing the Fire

Why it matters

The kitchen is silent — the gas knob is off. Turn it, click the lighter, and methane piped to the burner blooms into a clean blue flame. That blue is complete combustion: every CH₄ finishing as CO₂ and water vapour. Now count the atoms… the books don't balance yet.

The idea in plain words

Set the coefficients. Hint: fix carbon, then hydrogen, then let oxygen settle the account.

Predict first

In CH₄ + O₂ → CO₂ + H₂O, which elements are unbalanced as written?

C: 1=1 ✓, H: 4 vs 2 ✗, O: 2 vs 3 ✗. Balance H first (coefficient 2 on H₂O), then O follows (2 on O₂).

• Only carbon
• Hydrogen and oxygen — correct
• All three
• None — it's already balanced

What you do

Watch the burn, then balance it. Strategy: leave the lonely element (oxygen) for last.

Check yourself

The balanced equation for methane burning is…

C: 1=1, H: 4=4, O: 4=4. Option (a) leaves oxygen at 2 vs 4 — always recount every element after each change.

Why is it smart to balance oxygen LAST here?

Elements that appear alone (uncombined) are flexible — changing their coefficient touches nothing else. Lock the combined elements first.

This reaction releases heat and light. It is…

Energy out = exothermic. (It's a combustion reaction — reaction type and energy change are two separate labels.)

• CH₄ + O₂ → CO₂ + 2H₂O
• CH₄ + 2O₂ → CO₂ + 2H₂O — correct
• 2CH₄ + O₂ → 2CO₂ + H₂O
• CH₄ + 3O₂ → CO₂ + 2H₂O
• Oxygen is the heaviest element
• O₂ stands alone, so its coefficient adjusts freely without disturbing others — correct
• Oxygen doesn't really need balancing
• It's alphabetical order
• endothermic
• exothermic — correct
• a decomposition
• a physical change