Reaction Balancer
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flagWhat you'll discover
- arrow_forwardState the law of conservation of mass and what it means for equations
- arrow_forwardBalance chemical equations by adjusting coefficients — never subscripts
- arrow_forwardCount atoms of each element on both sides of a reaction
- arrow_forwardBalance real reactions including combustion and photosynthesis
Atoms are never lost
In 1789 Antoine Lavoisier weighed everything entering and leaving sealed reactions and found the totals always matched: mass is conserved. The modern explanation is simple — chemical reactions only rearrange atoms into new groupings; they never create or destroy them.
Burn a candle and the wax seems to vanish, but weigh the carbon dioxide and water vapour produced and every atom is accounted for. This law is the foundation of all chemical arithmetic: whatever atoms enter a reaction must come out the other side, just wearing different molecular outfits.
Coefficients, not subscripts
A balanced equation respects conservation by showing equal atoms of each element on both sides. You balance it by placing coefficients — the big numbers in front of formulas that multiply the whole molecule. 2H₂O means two complete water molecules: four H atoms and two O atoms.
The golden rule: never change the subscripts. Turning H₂O into H₂O₂ does not balance anything — it silently swaps water for hydrogen peroxide, a completely different chemical. The formulas are fixed by nature; your only legal move is choosing how many of each molecule take part.
A strategy that works
Balance like a detective, not by random guessing. Start with the element that appears in the fewest formulas — usually a metal or carbon — and leave lone elements like O₂ or H₂ for last, since their coefficients can be set freely at the end without disturbing anything else.
Try it on methane combustion: CH₄ + O₂ → CO₂ + H₂O. Carbon is already balanced. Four hydrogens on the left demand 2H₂O on the right. Now count oxygens on the right: 2 + 2 = 4, so the left needs 2O₂. Done: CH₄ + 2O₂ → CO₂ + 2H₂O. Finally, check the coefficients cannot all be divided down.
Balanced equations run the world
Balancing is not exam decoration — it is the recipe book of industry and life. Photosynthesis, 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, tells you a plant must capture exactly six CO₂ molecules for every glucose it builds, and that six O₂ come out — the oxygen you are breathing now.
Engineers use balanced equations to compute exactly how much oxygen a rocket must carry, how much lime neutralises a polluted lake, and how much CO₂ a power station emits per tonne of fuel. Every one of those calculations starts from the same idea you are practising here: count the atoms.