Download Balancing Chemical Equations

Balancing Chemical Equations
BELL RINGER: Answer the question into your
notebooks; make sure to write the examples, 1-8.
• Identify the following as an element or a
compound:
1. Na
2. NaF
3. Es
4. SiO
5. B
6. Ni
7. NaHCO3 8. MgCl2
Objectives
• Describe a chemical reaction by using a word
equation and a formula equation.
• Relate the conservation of mass to the
rearrangement of atoms in a chemical reaction
• Write and interpret a balanced chemical equation for
a reaction, and relate conservation of mass to the
balanced equation
What is a chemical equation?
• A chemical equation is a written symbolic
representation of a chemical reaction.
• The reactant chemical(s) are given on the left-hand
side and the product chemical(s) on the right-hand
side.
• Reactants: substance(s) that participates in a chemical
reaction
• Products: substance(s) that are produced during a
chemical reaction
What is a chemical equation? Contin….
• Here is an example of a chemical equation:
C3H8 + O2
Reactants
H2O + CO2
Products
• This reaction occurs when propane (C3H8) is burned in the
presence of oxygen to produce water and carbon dioxide.
Conservation of Mass
• The law of conservation of mass states that no
atoms can be created or destroyed in a
chemical reaction, so the number of atoms
that are present in the reactants has to
balance the number of atoms that are present
in the products.
• Reactants = Products
Write down the given chemical
equation.
• C3H8 + O2 --> H2O + CO2
Step 1: Write down the number of atoms per
each element that you have on each side of the
equation
• Look at the subscripts next to each atom to find the
number of atoms in the equation.
• C3H8 + O2 --> H2O + CO2
C=3
H=8
O=2
C=1
H=2
O=3
reactants
products
Step 2: Pick an element that is not equal on both sides of the
equation. Insert coefficients in front of the formula with that element.
Balance one element at a time. Count atoms of each element frequently
as you try different coefficients.
• In a chemical equation, you can change
coefficients, but you must never alter the
subscripts!
• C3H8 + O2 --> H2O + 3CO2
C=3
H=8
O=2
reactants
C=13
H=2
O=37
products
Step 3: Continue adding coefficients to get the same number
of atoms of each element on each side.
• In a chemical equation, you can change
coefficients, but you must never alter the
subscripts!
• C3H8 + 5O2 --> 4H2O + 3CO2
C=3
H=8
O=2
reactants
C=13
H=2
O=37
products
Step 4: Check your answer!
• C3H8 + 5O2 --> 4H2O + 3CO2
C=3
H=8
O = 10
reactants
C=3
H=8
O = 10
products
Practice Problems
1. P4 + O2
2. C3H8 + O2
3. Ca2Si + Cl2
P2O5
CO2 + H2O
CaCl2 + SiCl4
4. Silicon (Si) reacts with carbon dioxide(CO2)to
form silicon carbide,(SiC), and silicon dioxide
(SiO2).