Barrons SAT Subject Test Chemistry, 13th Edition

Looking at the oxygens, we see that there are an even number on the left but
an odd number on the right. This is a good place to start. If we use a coefficient of
2 for H 2 O, that will even out the oxygens but introduce four hydrogens on the right

while there are ten on the left. A coefficient of 5 will give us the right number of
hydrogens but introduces an odd number of oxygens. Therefore, we have to go to
the next even multiple of 5, which is 10. Ten gives us 20 hydrogen atoms on the
right. By placing another coefficient of 2 in front of C 4 H 10 , we also have 20

hydrogen atoms on the left. Now the carbons need to be balanced. By placing an 8
in front of CO 2 , we have eight carbons on both sides. The remaining step is to

balance the oxygens. We have 26 on the right side, so we need a coefficient of 13
in front of the O 2 on the left to give us 26 oxygens on both sides. Our balanced

equation is:

2C 4 H 10 + 13O 2 → 8CO 2 + 10H 2 O

TIP

Be sure you have included all sources of a particular element since it may occur in two or

more compounds.

SHOWING PHASES IN CHEMICAL EQUATIONS

Once an equation is balanced, you may choose to give additional information in
the equation. This can be done by indicating the phases of substances, telling
whether each substance is in the liquid phase (ℓ), the gaseous phase (g), or the
solid phase (s). Since many solids will not react to any appreciable extent unless
they are dissolved in water, the notation (aq) is used to indicate that the substance
exists in a water (aqueous) solution. Information concerning phase is given in
parentheses following the formula for each substance. Several illustrations of this
notation are given below:

Formula with Phase Notation

Meaning

Cl 2 (g)

Chlorine gas

H 2 O(ℓ)

Water in the liquid state as opposed to ice or steam

NaCl(s)

Sodium chloride as a solid