Chemical Formulas and Equations
Parts of a formula
 Coefficient: the number in front of the
symbol, which tells you how many
molecules there are.
 Subscript: The number after the
symbol, which tells you how many
atoms there are for each element.
Determining how many atoms
Multiply the coefficient by the
subscript
Use a 1 for any coefficient or
subscript that is missing
Example
5H2
1. Coefficient:
2. Subscript:
3. Element:
4. How many atoms?
Example
5H2
1. Coefficient: 5
2. Subscript: 2
3. Element: hydrogen
4. How many atoms? 5 x 2 = 10
Practice
3 CO2
2. N2O
3. 5MgCl2
4. 2 C6H12O6
1.
Try the ones on the back of the page!
Practice
3 CO2
2. N2O
3. 5MgCl2
4. 2 C6H12O6
1.
C = 3, O = 6
N = 2, O = 1
Mg = 5, Cl = 10
C = 12, H = 24, O = 12
Try the ones on the back of the page!
Chemical equations
A chemical equation is a short way to describe a chemical
reaction
Reactants: the starting materials in a chemical reaction (before
the arrow)
Products: the new substances made in a chemical reaction
(after the arrow)
Example: C + O2
CO2
Reactants: C (carbon) and O2 (oxygen)
Products: CO2 (carbon dioxide)
Chemical equations continued
 What does the arrow mean?
 Yields or gives you
 What does the “+” mean?
 “and”
 Law of conservation of mass:
 Atoms are not created nor destroyed
 You have to have the same number of each element on both
sides of the equation
Let’s practice
 Take out the last sheet you picked up on your way in
 Let’s do the first one together