Balancing Equations Review

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Balancing Equations

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To write a balanced chemical equation, first write the skeleton
equation. Then use coefficients to balance the equation so that it
obeys the law of conservation of mass.

This is a balanced equation for making a bicycle. The numbers
are called coefficients—small whole numbers that are placed in
front of the formulas in an equation in order to balance it.

Balancing Chemical Equations

Reactants appear on the
left side of the equation.

Products appear on the

right side of the equation.

The states of the reactants and products are written in parentheses
to the right of each compound.

Balancing Chemical Equations

1C
4H

1C
2O

2O

2H
1O

CH4(g)
O2(g)

+

CO2(g)

H2O(g)

+

Coefficients are inserted to balance the equation.

Balancing Chemical Equations

1C
4H

1C
2O

4O

4H
2O

CH4(g)
2O2(g)

+

CO2(g)

2H2O(g)
+

Subscripts and Coefficients

Subscriptsindicate the number of atoms of each element in a
molecule ­ changing the subscripts would change the type of
compound or molecule.

Coefficients tell the number of representative particles (atoms,
molecules, or formula units) ­ changing the coefficients just
changes the amount of a compound or molecule.

CH4(g)
2O2(g)

+

CO2(g)

2H2O(g)
+

2
2

1
1

H
Cl

reactants products

H2 + Cl2 HCl

H2 + Cl2 2HCl

Unbalanced

Balanced

2
2

2
2

H
Cl

reactants products

Balancing Chemical Equations

chlorine + sodium bromide bromine + sodium chloride

Balancing Chemical Equations

Write a balanced chemical equation for this reaction.

Cl2 + NaBr Br2 + NaCl

First write a skeleton equation.

Balancing Chemical Equations

Then, count up the number of each type of element on
each side of the reaction

Cl2 + NaBr Br2 + NaCl

Reactants

Products

Cl: 2

Cl: 1

Na:1

Na:1

Br: 1

Br: 2

Balancing Chemical Equations

Next, identify one element that is not balanced. It is best to start
with an easy element. The fewer places an element appears on
both sides of a reaction, the easier it will be to balance.

Cl2 + NaBr Br2 + NaCl

Reactants

Products

Cl: 2

Cl: 1

Na:1

Na:1

Br: 1

Br: 2

Balancing Chemical Equations

Identify the side that needs more of that particular element.

Cl2 + NaBr Br2 + NaCl

Reactants

Products

Cl: 2

Cl: 1

Na:1

Na:1

Br: 1

Br: 2

Balancing Chemical Equations

Determine which molecule or element needs an added
coefficient. In this case, add a coefficient to NaCl, since that is
the only product containing chlorine.

Cl: 2

Na: 1

Br: 1

Cl2 + NaBr Br2 + NaCl

Reactants

Products

Cl: 2

Cl: 1

Na:1

Na:1

Br: 1

Br: 2

Balancing Chemical Equations

To determine the coefficient, take the amount of that specific element
you need from the molecule, and divide by the amount of the element
you have in the molecule.

Cl2 + NaBr Br2 + __NaCl2

Need
Have

=2

1

= 2

Cl: 2

Na: 1

Br: 1

Reactants

Products

Cl: 2

Cl: 1

Na:1

Na:1

Br: 1

Br: 2

If this is not a whole number, multiply ALL the formulas in the reaction
by some whole number to make the coefficients whole numbers.

Balancing Chemical Equations

Now, just reevaluate the amount of each element on the table

Cl: 2

Na: 1

Br: 1

Cl2 + NaBr Br2 + 2NaCl

Reactants

Products

Cl: 2

Cl: 1 2

Na:1

Na:1 2

Br: 1

Br: 2

Balancing Chemical Equations

Continue with these steps until all the elements are balanced.
When all the elements exist in equal amounts on both sides of the
equation, you have a balanced chemical equation.

Cl2 + 2NaBr Br2 + 2NaCl

Cl: 2

Na: 1

Br: 1

Reactants

Products

Cl: 2

Cl: 1 2

Na:1 2

Na:1 2

Br: 1 2

Br: 2