1. Balancing Chemical Equations

2. Chemical Equations
A shorthand way to describe a chemical reaction using chemical symbols and formulae
It’s like a recipe for chemists.

3. Conserving matter Law of Conservation of Matter
matter is neither created nor destroyed in a chemical reaction, it is conserved
if you begin a reaction with 5 atoms of Hydrogen, you must end up with 5 atoms of Hydrogen

4. Parts of the Chemical Equation
Three Parts to a Chemical Equation
Reactants
substances present before the reaction
Yield Arrow
indicates the direction of a reaction
some reactions are reversible [double-sided arrow]
Products
substances present after the reaction

5. Chem. Equations – cont’d
Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants yields Products MgO + C CO + Mg magnesium oxide to form carbon monoxide reacts with carbon and magnesium

6. Chemical Equations – cont’d
Coefficient – (large) # in front of an element or molecule.
Ex: 4C
4 carbon atoms
ex: 5KI
5 potassium atoms & 5 iodine atoms
ex: 4SO4
4 Sulfur atoms & 16 Oxygen atoms (4x4)

7. Chemical Equations – cont’d
Subscript – (small) # to the lower right of an element
applies only to the element it is attached to
if outside of parentheses [(XY)3] applies to everything inside of parentheses
ex: H2
2 hydrogen atoms
ex: CO2
1 carbon atom, 2 oxygen atoms
ex: (SO4)3
3 Sulfur atoms (1x3), 12 Oxygen atoms (4x3)

8. Chemical Equations - cont’d
Try this:
Al2(SO4)3
Aluminum?
2 atoms
Sulfur?
3 atoms
Oxygen?
12 atoms (4x3)

9. Building a molecule Lets actually build H2 CO2 Al2(SO4)3
What happens if I put a coefficient in front?
Try it!

10. Balancing Chemical Reactions
Remember mass can not disappear so the number of atoms on one side of an equation must match the number of atoms on the other side of an equation.
To balance an equation you must:
Balance Coefficients.
You CAN NOT change a subscript.

11. Balancing – cont’d Al + S Al2S3 2Al + 3S Al2S3
Balanced = same # of each element on each side
Al S Al2S3
2Al S Al2S3
Unbalanced
Balanced

12. Balanced or Unbalanced?
C3H8 + 5O H2O + 3CO2
Carbon?
= 3 vs 3
Hydrogen?
= 8 vs 8
Oxygen
= 10 vs 10 (4 + 6)
Is it balanced?
Yes.

13. Balanced or Unbalanced?
Fe3O H Fe H2O
Iron
= 3 vs 1
Oxygen
= 4 vs 1
Hydrogen
= 2 vs 2
Is it balanced?
No.
So, now what?

14. Balancing a Chemical Reaction
Set up two columns: labeled “reactants” &“products.”
Identify & record reacting elements on the left.
Record product elements in the SAME ORDER on the right.
Count & Record # of each reacting element.
Count & Record # of each element produced.

15. Fe3O H Fe H2O

16. Balancing Chemical Reactions
To balance an equation you must:
Balance Coefficients. You CAN NOT change a subscript.
There are different ways to solve equations. Do what works best for you.
Way 1
change your greatest inequality first
leave solitary elements for last
Way 2
Simply work left to right, guess and check style.

17. Practice
Fe3O H Fe H2O

18. Practice
On your worksheet, complete the two problems on the front of your sheet.
____H2 + ____O2  ____H2O
____Cl2 + ____NaBr  ____Br2 + ____NaCl 2 1 2 1 2 1 2