1. Chemical Reactions and
Balancing Equations
March 27, 2013

2. Objectives
1. Explain the difference between
elemental and chemical formula
2. Recognize all the parts of a chemical
equation
3. Explain what is meant by a balanced
chemical equation
4. Demonstrate how to write simple
balanced chemical equations

3. Chemical Bonding
Chemical changes occur because of
breaking and rearrangement of chemical
bonds:
 The attraction between two atoms that holds
them together
Chemical change = chemical reaction

4. Chemical Equation
To show chemical reactions we use
chemical equations
C + O2  CO2
4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)

5. Parts of Chemical Equation
Elemental formula: how atoms are
bounded together in an element

Li
 O2 , N2 , S8

6. Chemical formula: representation
of a compound, when atoms of
different elements bond to each other
 NaCl, NH3 , CO2

7. Coefficient:
represents how
many of a
particular element
or molecule
Subscript:
represents how
many of a
particular atom

8. How many atoms?
C + O2  CO2
4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)

9. (s) represents solid
(l) represents liquid
(g) represents gas
(aq) represents aqueous

10. Chemical Equation
Reactants  Products
C + O2  CO2
when reading an equation Arrow = yields

11. Agenda Bell Work
• Finish balancing • Review for quiz
notes
• Practice
• Ionic Puzzle Piece
activity

12. Law of Conservation of Mass
Matter is neither created nor destroyed
during a chemical reaction
Therefore all chemical equations must be
balanced; equal atoms of each element on
each side

13. Balancing equation rules
You may change the coefficients in front
You may NOT change the subscripts
Changing the subscript changes the
compound

14. Steps of balancing
1. Write the correct formulas for the
equation. Once written do not change
the formula’s
2. Find the number of atoms on the left side
of each element and compare it against
the number of atoms of the same
elements on the right side

15. 3. Determine where to place coefficients in
front of formulas so that the left side has
the same number of atoms as the right
side for EACH element in order to
balance the equation.

16. 4. Check your answer to see if:

The numbers of atoms on both
sides of the equation are now
balanced.
 The coefficients are in the lowest
possible whole number ratios.
(reduced)

17. Helpful hints
Take one element at a time working left to
right,
Leave H for next to last and O last
IF everything balances except for O, and
there is no way to balance O with a whole
number, double all the coefficients and try
again.

18. Balancing Equations
___ H2(g) + ___ O2(g) ---> ___ H2O(l)
One of the oxygen atoms
binds with two of the
hydrogen atoms

19. Done Activities
Which equations are balanced?
Balance the ones that aren’t
a.Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
b. 3Al(s) + 3Br2(l)  Al2Br3(s)
c. 2HgO(s)  2Hg(l) + O2(g)

20. ___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

21. ____C3H8(g) + _____ O2(g) ---->
_____CO2(g) + _____ H2O(g)
____B4H10(g) + _____ O2(g) ---->
_____B2O3(g) + _____ H2O(g)