Chemical Reaction Notes + Practice
Writing a balanced chemical equation is one of the most crucial skills needed for success as a chemist and chemistry
student alike. By writing balanced chemical equations, chemists are able to determine a variety of useful
information, including the heat generated or consumed during a reaction, the amount of product being produced,
and the state of matter of reactants and products. Additionally, a balanced chemical equation assists chemists in
determining the rate at which the reaction occurs, the voltage given off from an electrochemical circuit, and how
certain solutions will respond to the removal or addition of certain chemicals. The first step in writing a balanced
equation is to take a word equation and convert it to a chemical equation. For example: “solid sodium combines
with chlorine gas to produce solid sodium chloride,” would be the word equation. Converting to a chemical equation
would look something like: 2 Na(s) + Cl2(g) ⟶ 2 NaCl(s).
Why did chlorine become Cl2 and not simply Cl? There are seven elements that are more stable as a diatomic
molecule (a molecule composed of only two elements). The seven are shown below:
Hydrogen
H2
Oxygen
O2
Nitrogen
N2
Chlorine
Cl2
Bromine
Br2
Iodine
I2
Fluorine
F2
An easy way to remember them is to think of the acronym HONClBrIF (honklebrif). If any of these seven molecules
are mentioned by themselves in a chemical equation, they must be written as a diatomic molecule. For example: “
Ammonia (NH3) gas reacts with oxygen gas to produce nitrogen monoxide gas and water vapor,” would be written
as: NH3(g) + O2(g) ⟶ NO(g) + H2O(g).
When writing chemical equations, it is important to recognize if the compounds present are covalent, ionic, or acidic,
as each has their own rules for writing formulas. The following table will help to summarize how to identify each and
how to write their formula.
Type of Compound
Identifier
Tips/Tricks
Covalent
Nonmetal + nonmetal
Use prefixes to write subscripts
Ionic
Metal + nonmetal
Write charges of both and criss-cross
Acidic
Hydrogen in front
H+ + _________
“Big name = small ion (periodic table)”
“Small name = big ion (polyatomic)
“What we ate was ic but it was ite with ous”
Metallic
Metal solid
The formula for solid metals is just the metal
atom (NO subscripts). Ex: Magnesium metal is
Mg(s).
Chemical Reactions Practice: Writing and Balancing Equations
For the following 12 word equations, write 8 of them as balanced chemical reactions. Be sure to watch for the
diatomic molecules (HONClBrIF). Include states of matter in parenthesis: solid (s), liquid (l), gas (g), aqueous (aq).
On the bottom of this paper, translate the word equation into a chemical equation AND balance it.
Choose 8 of the 12
1. When solid copper reacts with aqueous silver (I) nitrate, the products are aqueous copper (II) nitrate and
silver metal.
2. Solid iron (III) oxide and carbon monoxide gas produce iron metal and carbon dioxide gas.
3. Aqueous sulfuric acid and solid sodium hydroxide react to form aqueous sodium sulfate and water.
4. Solid chromium (II) oxide and iron (III) oxide react to form solid chromium (V) oxide and iron (II) oxide.
5. Aluminum metal reacts with oxygen gas to produce solid aluminum oxide.
6. Solid mercury (II) oxide decomposes to produce liquid mercury and oxygen gas.
7. Powdered sodium carbonate decomposes to produce solid sodium oxide and carbon dioxide gas.
8. Carbon dioxide gas reacts with solid lithium hydroxide to produce solid lithium carbonate and water.
9. Solid ammonium nitrate decomposes to produce dinitrogen monoxide gas and water.
10. Carbon monoxide gas reacts with hydrogen gas to produce liquid methanol (CH3OH).
11. Liquid carbon disulfide reacts with oxygen gas to produce carbon dioxide gas and sulfur dioxide gas.
12. Aluminum metal reacts with aqueous copper (II) chloride to produce aqueous aluminum chloride and solid
copper.