Balancing Chemical Equations

Demonstration!!!!!!!!

Sentence - Combine dissolved Lead (II) Nitrate with aqueous Potassium Iodide to yield aqueous Potassium Nitrate and solid Lead (II) Iodide

Word - ____

Chemical- _____

This is called a double displacement reaction more on this to come.

Balanced Chemical Equations

• Atoms can’t be created or destroyed in a reaction:–All the atoms we _________we must

___________(meaning: balanced!)• A balanced equation has the same

number of each element __________of the equation.

Chemical ReactionsWhile the reactions show what is used up and what is produced, they do not

reflect the proper number of each type of atom required for the reaction.

H2 + O2 H2O

How many oxygen atoms are on the right?____How many oxygen atoms are on the left?____Does this make sense? What happened to that other oxygen atom.We use coefficients to “balance the equation” ensure that there are the same

number of each type of atom on either side of the equation.Afterwards check to make sure the number of atoms on the left = the right

**Using coefficients doesn’t change the reaction, it simple shows us how many atoms were actually involved**

2 2

Rules for balancing:1) Assemble the _____________ for all the

reactants and products, using “+” and “→”2) Count the number of atoms of each type

appearing on both sides3) Balance the elements one at a time by adding

coefficients (the numbers in front) where you need more - _______________________________________(hint: I prefer to save O until the very last)

4) _________ to make sure it is balanced by counting the atoms on both sides.

• _______change a subscript to balance an equation (You can only change coefficients)– If you change the subscript (formula) you are

describing a different chemical.– H2O is a different compound than H2O2

• _______ put a coefficient in the middle of a formula; they must go only in the _______

__NaCl is okay, but Na__Cl is not.

Chemical Reactions

In more complicated chemical reactions, we may want to use a chart to keep track of the number of each kind of atom,

CH4 + O2 CO2 + H2O

Now lets count the atoms,To balance Hydrogen.Try putting a 2 in front of the H2O

To balance OxygenTry putting a 2 in front of the oxygen

Element Before After

C 1 1

H 4 2

O 2 3

Element Before After

C 1 1

H 4 4

O 2 4

Element Before After

C 1 1

H 4 4

O 4 4

_ _

Chemical Reactions

Some more practice.

N2 + H2 NH3

If there is a polyatomic that sticks together than you can balance it as a whole.Pb(NO3)2+ KI PbI2 + KNO3

NaHCO3 + H2SO4 Na2SO4 + H2O + CO2__ ____

____

____

Practice Balancing Examples

• _AgNO3 + _Cu _Cu(NO3)2 + _Ag

• _Mg + _N2 _Mg3N2

• _P + _O2 _P4O10

• _Na + _H2O _H2 + _NaOH

• _CH4 + _O2 _CO2 + _H2O