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PEAZIT Aha card

Chemical equations: keep every atom

Change the number of whole particles, not their composition.

Atom counts for 2 H₂ + O₂ → 2 H₂O.

Atom	Left	Right
H	4	4
O	2	2

One worked example

H₂ + O₂ → H₂OOxygen is not balanced yet.
H₂ + O₂ → 2 H₂OTwo water molecules contain two oxygen atoms and four hydrogen atoms.
2 H₂ + O₂ → 2 H₂OTwo hydrogen molecules supply the four H atoms.

Watch out: Do not change subscripts: H₂O₂ is a different substance from H₂O. Balancing does not establish reaction speed or conditions.

Goal, prerequisites and card origin

What you will learn: Balance a simple equation without changing formulas.

What you need first: Element symbols and atom counts from formula subscripts.

An original PEAZIT working card. Independent expert review and effectiveness testing have not yet taken place. · v1

OpenStax Chemistry 2e, 4.1 (content source supplied in methodology) ↗

Show connections

Chemical equations conserve atoms

H₂ molecule — we need two molecules — 2 H₂ + O₂ → 2 H₂O

O₂ molecule — we need one molecule — 2 H₂ + O₂ → 2 H₂O

2 H₂ + O₂ → 2 H₂O — two molecules are formed — H₂O molecule

H₂O molecule — hydrogen is conserved: 4 atoms on each side — H₂ molecule

H₂O molecule — oxygen is conserved: 2 atoms on each side — O₂ molecule

Change the number of whole particles, not their composition.

Without JavaScript, write your answer elsewhere before opening the solution.Balance N₂ + H₂ → NH₃ with the smallest whole-number coefficients. Enter the three numbers separated by commas, in this order.

Solution — open after your own attempt

1, 3, 2 N₂ + 3 H₂ → 2 NH₃. Each side has 2 N atoms and 6 H atoms.

A question for your next return: Balance Mg + O₂ → MgO with the smallest whole-number coefficients. Enter three numbers separated by commas.

Solution — open after your own attempt

2, 1, 2 2 Mg + O₂ → 2 MgO. Each side has 2 Mg atoms and 2 O atoms.

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