Balancing chemical equations
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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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Balancing chemical equations

Balancing Chemical Equations


A balanced equation

A “balanced” equation

Has equal numbers of atoms of each element in the reactants and in the products.


How do you balance an equation

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


How do you balance an equation1

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


Using coefficients

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


How many atoms are indicated by the formula

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


Some pointers in balancing

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


Some pointers in balancing1

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


Examples in reactions

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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