1. Law of Conservation of Mass:
BALANCING EQUATIONS NOTES
A way to represent chemical reactions on paper
DO NOT WRITE ON THIS PAPER. COPY THE NOTES IN YOUR NOTEBOOK Chemical Equations:
Law of Conservation of Mass:
Mass is neither created nor destroyed during a chemical reaction- it is conserved.
Mass reactants = Mass products

2. Chemical Equations/ Law of Conservation of Mass
For an equation to follow the Law of Conservation of Mass, the equation must be balanced.
Atoms can neither be created nor destroyed in an ordinary chemical reaction, so there must be the same number of atoms on both sides of the equation

3. Numbers found in a chemical reaction
Subscripts-
The small numbers to the lower right of chemical symbols. Subscripts represent the number of atoms of each element in the molecule.
Example 1: How many atoms of each element are in one formula unit of Calcium Nitrate: Ca(NO3)2 ?
Ca= N= O= 6
Example 2: How many atoms of each element are in one formula unit of Magnesium Oxide: MgO ?
Mg= O = 1

4. Numbers found in a chemical reaction
Coefficients
The large numbers in front of chemical formulas. Coefficients represent the number of molecules of the substance in the reaction.
Example 1: How many atoms of each element are there in 3 formula units of Calcium Nitrate: 3Ca(NO3)2 ?
Ca= N= O= 18
Example 2: How many atoms of each element are there in 2 formula units of Magnesium Oxide: MgO
Mg= O= 2

5. Writing Chemical Equations
Check for diatomic molecules:
H2, N2, O2, Cl2, F2, Br2, I2
If these elements appear by themselves in an equation, they must be with the subscript 2.
Chemical Equations give information in 2 major areas:
They tell us what substances are reacting and what substances are being produced.
Reactants  Products
Example: 2 H2+ O2  2H2O, What are the reactants and what are the products?
Reactants: H2 and O2
Products: H2O

6. ASSIGNMENT 2. ____H2 + _____Cl2 → _____HCl
1. Aluminum metal reacts with oxygen to form solid aluminum oxide.
2. ____H2 + _____Cl2 → _____HCl
3. _____HCl + _____Fe2O3 → _____FeCl3 + _____H2O
4. _____MgCl2 → ______Mg + ____Cl2