BALANCING CHEMICAL EQUATIONS
Subscript – a number that goes on the bottom of an atom that tells us the atoms are glued together. You
CANNOT change a subscript in balancing a chemical equation
COEFFICIENT - a number that goes in front of an atom or compound that tells us how many of them
we have
So far, we have been doing simple reactions – adding one element or compound to another to make
something new…These are called synthesis reaction
It is now time to move on toe balanced reactions and balanced equations that more correctly show what
actually happens in a chemical reaction.
LAW OF CONSERVATION OF MASS
This law says that the total amount of atoms must always be the same before and after a
Chemical reaction because…ATOMS CANNOT BE CREATED OR DESTROUYED UNDER
ORDINARY CIRCUMSTANCES
The Steps to use in balancing a chemical reaction
Step 1
Check the valences to be sure the compounds are correct and fix any diatomic gasses –
necessary. (Remember! Gases do NOT travel alone )
Step 2
Count all the atoms of the reactants and products
Step 3
Pick an element that is NOT equal and add a COEFFICIENT
Step 4
Continue adjusting coefficients until it all balances – same number of atoms on each
side of the equation (reactants and products)
Note *
If a compound starts with “H” (hydrogen) it is probably an ACID
NEVER change SUB-SCRIPTS!
Adjust/balance an equation by inserting COEFFICIENTS
NOTE:**
To balance an equation, count the atoms on each side of the equation (reactant side and
product side). They must be the same on each side. If they are not, use Coefficients ONLY to balance the
number of atoms on each side…remember!! CANNOT change subscripts!
Kinds of Reactions
Synthesis Reactions - 2 or more single elements come together to form a compound
Example
H2 + O2
2H2 + O2
------->
-----_>
H2 O
2H2O
Single Displacement Reactions - one metal knocks another metal out of a compound and takes its place
Example
Na + H2O ------->
2Na + 2H2O ----
NaOH + H
2NaOH + H2
Double Displacement Reaction - 2 metals switch places
Example
FeCl + NH4OH --- Fe(OH) + NH4Cl
2FeCl3 + 3NH4OH ---- Fe(OH)3 + 3NH4Cl
Decomposition Reaction - A compound gets broken down into simpler parts
Example
KClO3 ---
KCl + O2
2KClO3 ---->
NOTE!**
2KCl + 3O2
To fully understand how to balance chemical equations YOU MUST PRACTICE!!
See me for individual instruction if you are not getting this!