Figure 1.0 – The Anatomy of a Chemical Equation

The chemical formulas for the reactants, which are combined in the reaction, are written first (on the left side of the chemical equation). A plus sign is inserted between each formula to indicate they are combined. An arrow pointing right is written after the reactants. This arrow represents “yields” or “produces” when reading a chemical reaction. The chemical formulas for the products, which are created in the reaction, are written after the arrow (on the right side of the chemical equation). A plus sign is also used between the chemical formulas for the products.

To better illustrate what reaction occurs between ions in chemical reactions, compounds are written in the form in which they are predominantly present in water. To illustrate the phase of matter each chemical is present in, subscript letters are used after the chemical formula. (aq) means the chemical is dissolved in an aqueous solution. (s) means the chemical is a solid. If that chemical is a product, then a precipitate has formed. (g) means the chemical is a gas. (l) means liquid. This designation is typically reserved for water and organic solvents used in a reaction.

Chemical reactions are then balanced by adding whole numbers in front of the chemical formulas. Remember that nothing can be changed about the chemical formula to balance an equation. We can only change the number of moles (or molecules) of each compound present in the reaction.

Now that we know the basic organization of a chemical reaction, let’s review the major types of chemical reactions.

Classifying Types of Chemical Reactions

There are 5 basic types of chemical reactions. Being able to recognize when each of these reactions occurs aids in predicting the products that form.

Combination Reaction

These reactions occur when two substances combine to make a single new substance. Combination reactions follow the general formula:

A + B → AB

Decomposition Reaction

Decomposition reactions occur when a compound breaks into two new substances. Decomposition reactions follow the general formula:

AB → A + B

Decomposition and combination reactions are the opposite of each other.

Single-Replacement Reaction

Single-replacement reactions occur when an element reacts with a compound. One of the elements within the compound is replaced by the element it is reacting with. Single replacement reactions follow the general formula:

A + BC → B + AC

Double-Replacement Reaction

Double-Replacement Reactions (aka the Do-si-do Reaction) involve the reaction of two compounds. The cations in each compound exchange anion partners, forming two new compounds. Double-replacement reactions follow the following formula:

AB + CD → AD + CB

Combustion

Combustion reactions occur when a compound reacts with oxygen gas to produce heat energy.  Typically, hydrocarbons (compounds made only of carbon and hydrogen) are involved in these reactions; however, combustion can also occur with other compounds. The complete combustion of hydrocarbons always produces carbon dioxide and water. Below is the basic formula for a hydrocarbon reaction:

Hydrocarbon + O₂ → CO₂ + H₂O

Below is a generic reaction of a combustion reaction that does not involve a hydrocarbon, where A is the element reacting with oxygen.

A + O₂ → AO

Notice how the above combustion reaction also resembles a combination reaction. Simply replace the O with B, and they follow the same formula. This means that a combustion reaction may also be a combination reaction

Combination Reaction: A + B → AB

This Week’s Lab

You will organize your data for this lab into a data table. Click below for a copy of the data table you will need for this lab. This is an editable MS Word document. All of your data from this week’s experiment must be recorded into this data table, not a reproduction. It will download to your computer. If you have trouble downloading it, check to ensure blockers are disabled.

Writing Chemical Reactions Data Table

Safety Concerns

No hazardous chemicals are used in this experiment.

Acetic Acid (vinegar) is a weak acid and can cause skin irritation if prolonged contact occurs. Avoid contact with skin and eyes. See the Safety Data Sheet for more information.

You will use a lighter in this lab. Pull back long sleeves, remove any loose-hanging clothing such as long necklaces and scarves, tie back long hair, and remove all hats before using the lighter. Have a fire extinguisher easily accessible as a precautionary measure.