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Balancing Chemical Equations

Balancing Chemical Equations. A “balanced” equation. Has equal numbers of atoms of each element in the reactants and in the products. How do you balance an equation?. You cannot change subscripts: Ex: H 2 O is water H 2 O 2 is hydrogen peroxide These are obviously not the same thing.

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Balancing Chemical Equations

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  1. Balancing Chemical Equations

  2. A “balanced” equation Has equal numbers of atoms of each element in the reactants and in the products.

  3. How do you balance an equation? • You cannot change subscripts: • Ex: H2O is water • H2O2 is hydrogen peroxide • These are obviously not the same thing

  4. How do you balance an equation? The only “tool” at your disposal in balancing equations is a “coefficient” • Whole number • Written to the left of a formula • Multiplies the number of atoms of each element present in the compound

  5. Using coefficients Consider: NaNO3 (sodium nitrate) • Formula indicates: 1-Na, 1-N, 3-O Now consider: 4 NaNO3 • Coefficient indicates 4 times as many of everything • Therefore, 4-Na, 4-N, 12-O

  6. How many atoms are indicated by the formula: Mg3(PO4)2 • 3-Mg, 2-P, 8-O 3 Mg3(PO4)2 • Three times as many of everything • 9-Mg, 6-P, 24-O

  7. Some pointers in balancing • Only balance one element at a time • Use a pencil • easier to change coefficients as needed • Leave oxygen for last • Leave hydrogen for second to last

  8. Some pointers in balancing Reduce the coefficients if they can all be divided by the same number Ex:2 P4 + 10 O2 4 P2O5 Coefficients should be divided by 2 and written P4 + 5 O2 2 P2O5

  9. Examples in reactions… • sulfur + oxygen yields sulfur dioxide • S8 + O2 SO2 …is this balanced? • S8 + 8 O2 8 SO2 • How about… diphosphorus pentoxide decomposes into phosphorus and oxygen? • P2O5  P4 + O2 • 2 P2O5  P4 + 5 O2

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