Intro to Chemical Equations and Reactions
Name ____________________________
Chemical Equations use symbols and formulas to how substances change during a reaction:
Reactants:
The elements or compounds that we start with.
Products:
The elements or compounds that are produced in a chemical reaction.
Law of Conservation of Matter (Mass): Equations are balanced to uphold this law.
 Atoms are neither created nor destroyed during ordinary chemical change. The atoms are simply
rearranged.
 The total number of atoms before the reaction is equal to the total number of atoms after the reaction.
REVIEW OF FORMULAS – Coefficients and Subscripts
Formula
How many of each type of atom in ONE
molecule?
How many of the whole
Molecule?
How many total
Na2O
2Na2O
4Na2O
S’MORES FORMULAS:
1. Write the formula for one s’more: _____________________
2. Write the formula for two s’mores: _______________________
On your formula above, draw a square around the coefficient.
Draw a circle around the subscripts.
3. If you have two s’mores how many of each type of “atom” do you have?
_____ Gc
_____ M
_____Cp
4. Describe in words EVERYTHING a person can tell from this formula: 3Gc 2MCp3
5. Complete chemical equation for the making of a s’more. The reactants go on the left and the product on the
right.
_______ Gc + _______ M + _______ Cp  __________________
6. How do s’mores relate to chemical formulas? (Use complete sentences.)
Balancing Chemical Equations: Equations are balanced to uphold the Law of Conservation of Matter.
To balance a chemical equation:

First, if the equation is not complete, write out the correct formulas…
1. Use charges
2. Know the 7 Diatomic Elements: Make sure you know which elements are diatomic so you can
write the correct equation.

Diatomic elements are elements so reactive that they react with themselves
H2 , N2 , O2 , F2 , Cl2 , Br2 , I2

Second, add coefficients to make sure each element total on the reactant side is equal to element total on
the product side. (Do not change subscripts when balancing!)
Example: Write the equation for hydrogen and oxygen reacting to form water.
Make a s’more and then balance these equations!
Balancing – These start easier and get harder as you go. REMEMBER: Do not add/change subscripts!
1.
Ca
2.
NaCl
3.
Mg
4.
WO
5.
CS2
+
O2

+
+
+

CaO
Na
+
Cl2
HCl

MgCl2
H2

W
+
H2O

CO2 +
SO2
O2
6.
HCl
+
NaOH
7.
Na2O
+
H2O


+
NaCl
NaOH
H2
+
H2O
8.
CaC2
+
H2O

Ca(OH)2 +
C2H2
9.
CO2
+
H2O

C6H12O6 +
O2