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82 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 9
Practice Problems
1. Write a word equation and a skeleton equation for each of the
following descriptions of chemical reactions.
a. Solid lithium reacts with chlorine gas to produce solid
lithium chloride.
b. Nitrogen gas reacts with oxygen gas to produce nitrogen
dioxide gas.
c. Solid iron reacts with aqueous copper(II) nitrate to produce
solid copper and aqueous iron(II) nitrate.
Balanced chemical equations Skeleton equations do not reflect
the fact that matter is conserved during a reaction. In actual chemical
reactions, atoms are neither created nor destroyed but are conserved.
An equation that reflects the fact that the same number of each kind
of atom must appear on both sides of the arrow is called a balanced
chemical equation. It uses chemical formulas to show the identities
and relative amounts of the substances involved in a reaction.
To balance a chemical equation, you write coefficients, which
are numbers placed in front of the chemical formulas. The lowest
whole-number ratio is used. If no coefficient appears next to a formula, the number 1 is understood. The steps involved in balancing a
chemical equation are as follows.
Step 1 Write the skeleton equation.
Step 2 Count the atoms of the elements in the reactants. Any
polyatomic ions that remain unchanged can be counted as if they
are elements.
Step 3 Count the atoms of the elements in the products.
Step 4 Change the coefficients to make the number of atoms of
each element equal on both sides of the equation. Do not change
subscripts.
Step 5 Write the coefficients in their lowest possible ratio.
Step 6 Check your work.
▲
82 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 9
Practice Problems
1. Write a word equation and a skeleton equation for each of the
following descriptions of chemical reactions.
a. Solid lithium reacts with chlorine gas to produce solid
lithium chloride.
b. Nitrogen gas reacts with oxygen gas to produce nitrogen
dioxide gas.
c. Solid iron reacts with aqueous copper(II) nitrate to produce
solid copper and aqueous iron(II) nitrate.
Balanced chemical equations Skeleton equations do not reflect
the fact that matter is conserved during a reaction. In actual chemical
reactions, atoms are neither created nor destroyed but are conserved.
An equation that reflects the fact that the same number of each kind
of atom must appear on both sides of the arrow is called a balanced
chemical equation. It uses chemical formulas to show the identities
and relative amounts of the substances involved in a reaction.
To balance a chemical equation, you write coefficients, which
are numbers placed in front of the chemical formulas. The lowest
whole-number ratio is used. If no coefficient appears next to a formula, the number 1 is understood. The steps involved in balancing a
chemical equation are as follows.
Step 1 Write the skeleton equation.
Step 2 Count the atoms of the elements in the reactants. Any
polyatomic ions that remain unchanged can be counted as if they
are elements.
Step 3 Count the atoms of the elements in the products.
Step 4 Change the coefficients to make the number of atoms of
each element equal on both sides of the equation. Do not change
subscripts.
Step 5 Write the coefficients in their lowest possible ratio.
Step 6 Check your work.
▲