Download Balancing Equations

Polyatomic Ions
• Polyatomic ions- a unit of more than one atom
• Ways to identify polyatomic ions….
1. If you see elements in parentheses, these are the poly atomics
Ca(OH)2
Be(NO3)2
(NH4)2S
2. If you find the polyatomic ion on your polyatomic ions sheet!
Balancing Equations
Subscripts
Coefficient
PRODUCTS
REACTANTS
YIELD SYMBOL
Subscripts
Subscripts
Coefficient
2CU + Zn(NO3)2  2CuNO3 + Zn
Chemical Reaction Vocabulary
• Chemical Reaction: One or more reactants change into one or more
products
• Reactant: A substance present at the start of a reaction
• Product: A substance produced in a chemical reaction
• Chemical Equation: An expression representing a chemical reaction;
the formulas of the reactants (on the left) are connected by an arrow
with the formulas for the products (on the right).
• Example: Reactants
Products
Law of Conservation of Mass
In a chemical reaction mass is conserved.
•Mass cannot be created or destroyed
•It can only change forms
• Solid to liquid to gas
• Change into another substance
Example
• Before
Which one has the greater mass?
• After change
Law of Conservation of Mass —Mass is
never created or destroyed in a chemical
reaction.
•
•
•
When material is burned, residue is less massive than
original material
Ash, smoke, and gases escaped into the air—(they are
still considered matter.)
Their mass was not lost, only relocated due to the law of
conservation of mass.
Law of Conservation of Mass
We learned how to count atoms in a
chemical formula,
now we have to make sure we have the
same amount of atoms on each side of the
reaction.
Balancing Chemical Equations
A chemical equation in which mass is conserved; each side of the
equation has the same number of atoms of each element
Is this equation balanced?
Fe + O2
Fe2O2
How many….on the reactants side?
On the products side
Fe
Fe
O
O
The iron is not balanced to conserve mass. We have 1 on the left and 2 on the right,
so we need to at a coefficient (small whole number that are placed in front of the
formulas in an equation in order to balance it). So the equation would look like this:
2Fe + O2
Fe2O2
Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients as needed to make #s equal on
both sides of the equation.
Coefficient  subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if
necessary.
5. Double check atom balance!!!
Helpful Tips
• Balance one element at a time.
• Update ALL atom counts after adding a coefficient.
• If an element appears more than once per side,
balance it last.
• Balance polyatomic ions as single units.
• Common poly atomics: SO4,PO4,CO3,OH
• Example: “1 SO4” instead of “1 S” and “4 O”