Ok well here is an example...
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(Preview)
SnO2 + H2 -> Sn + H2O
Here is the starting chemical equation. You need the same ammount of atoms on each side of each atom. So you need the same ammount of "Sn" on each side. And "O". And "H". And so on and so forwth.
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(Answer)
SnO2 + 2H2 -> Sn + 2H20
So here is the answer to balance out the equation.
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(Review)
Notice I put a 2 in front of H2 and H2O. Now there is...
(1)Sn (2)O (4)H
Hope that helped a bit! (On how to do it of course)
-Complex