Anatomy of a Balanced Chemical Equation:

Pb(NO₃)_2(aq) + Na₂O_(aq) --> 2 NaNO_3(aq) + PbO_(s)

Arrow: yields or produces; located in between the reactants and products

Reactant/reactants: located left of the arrow; substances participating in the chemical reaction; Pb(NO₃)_2(aq) + Na₂O_(aq)

Product/products: located right of the arrow; substances resulting from a chemical reaction; NaNO_3(aq) + PbO_(s)

Subscript: Subscripts can mean different things. Some are part of the formula for a polyatomic ion and some are telling you the number of atoms or ions. For example, Pb(NO₃)_2(aq) has a subscript of 3 on the oxygen and a subscript of 2 outside the parentheses. The 3 in NO₃ means there are three oxygen atoms as a part of the polyatomic nitrate ion (NO₃). The subscript of 2 outside the parenthesis says that in this particular chemical formula, Pb(NO₃)₂, there are two nitrate ions.

Chemical formula: describes how many atoms/ions are in a substance

Coefficient: tells how many molecules or formula units of a substance are needed

Note: You never write in a coefficient of 1.

State of matter: symbol showing what state the substance currently exists in

Helpful hints to balancing equations:

1. Balance the different types of atoms one by one

2. First balance atoms that only show up once on each side

3. Balance polyatomic ions that appear on both sides as a single unit (you may use a substitution method if it is easier for you)

4. Balance H and O after all other atoms. These typically show up the most, thus are most difficult to balance. As a general rule of thumb, if an element is in more than one place on a given side of the equation, save it for last.

Key point: “balanced” means there are the same number of each element on each side

There are two methods for balancing chemical equations: inspection and inventory.

2 Methods:

• Method 1 = Inventory:

Step #1: Set up an inventory. Draw a line down from the arrow to separate the reactants and products. Write the symbol for each element (or polyatomic ion) present on both sides of the equation. Reactants go left of the line you just drew and products go right of the line you just drew. You don’t have to line them up, but I think it makes your life easier to do so. Note the subscripts next to each element or polyatomic ion and write that number next to the element symbols.

Step #2: Pick one element (or polyatomic ion) and determine what you need to get them to balance. Remember, “balance” means there are the same number of each element on each side. The number you determine you need to multiply a certain compound by gets written to the left of the compounds as a coefficient.

Tip: If a polyatomic ion is on both sides of the equation, leave them together. It makes those elements easier to track.

Step #3: Be sure to adjust your inventory to reflect the coefficient’s effect on the entire compound

Step #4: Repeat steps #2 and #3 until each element or polyatomic ion is balanced.

• Method 2 = Inspection:

You pick an element (or polyatomic ion) and balance it. Then you see what that changes and balance something else. It helps if you find a set system of how to approach them (ie. left to right, unless it's one of the special cases).

Five Types of Chemical Reactions:

Synthesis: two substances coming together to form one product

Decomposition: one substance breaking down into two or more products

Single replacement (single displacement): an element and a compound reacting to form a different element and a different compound

Double replacement (double displacement): two compounds reacting to form two different compounds

Combustion: a compound reacting with oxygen that results in the release of energy

Note: in my college prep course, we stick to general hydrocarbons so the resulting products are carbon dioxide and water