1. Balancing Chemical Equations

2. Law of Conservation of Mass
Balanced Equation
Atoms can’t be created or destroyed
Law of Conservation of Mass
All the atoms we start with we must end up with
A balanced equation has the same number of each element on both sides of the equation (reactant and product sides).

3. Counting Atoms 2H2 + O2  2H2O Subscript: (numbers below)
Reactants  product
Subscript: (numbers below)
indicates how many atoms of an element.
Coefficient (numbers in front)
Indicates how many molecules/moles of a compound
(multiplies the number of atoms of each element in the compound)

4. Chemical Formula
Counting up Atoms

5. Let’s Practice NH3 NaCl _____ atoms of Nitrogen
_____ atoms of Hydrogen
_____ molecules/moles of NH3
NaCl
_____ atoms of Sodium
_____ atoms of Chlorine
_____ molecule/moles of NaCl

6. Practice NH3 NaCl __1___ atoms of Nitrogen __3___ atoms of Hydrogen
__1__ molecules/moles of NH3
NaCl
__1___ atoms of Sodium
__1___ atoms of Chlorine
__1___ molecule/moles of NaCl

7. Practice Again 8NaCl 3NH3 Ca(NO3)2 _____ atoms of Sodium
_____ atoms of Chlorine
_____ molecule/moles of NaCl
3NH3
____ atoms of Nitrogen
____ atoms of Hydrogen
___ molecule/moles of NH3
Ca(NO3)2
_____ atoms of Calcium
_____ atoms of Nitrogen
_____ atoms of Oxygen
_____molecule/moles of Ca(NO3)2

8. Practice Again 8NaCl 3NH3 Ca(NO3)2 __8___ atoms of Sodium
__8___ atoms of Chlorine
__8___ molecule/moles of NaCl
3NH3
__3__ atoms of Nitrogen
__9__ atoms of Hydrogen
__3_ molecules/moles of NH3
Ca(NO3)2
___1__ atoms of Calcium
___2__ atoms of Nitrogen
___6__ atoms of Oxygen
___1__molecule/moles of Ca(NO3)2
What if there is a coefficient of 2 in front of Ca(NO3)2 ?

9. More Practice SO2 + 3H2O _____ atoms of Sulfur _____ atoms of Hydrogen
_____ atoms of Oxygen
_____ molecule/moles of SO2
_____ molecules of H2O

10. More Practice SO2 + 3H2O __1___ atoms of Sulfur
__6___ atoms of Hydrogen
__5___ atoms of Oxygen
__1___ molecule/moles of SO2
__3___ molecules of H2O

11. Let’s Step It Up a Little
2NH4NO3 + 3H2S
_____ atoms of Nitrogen
_____ atoms of Hydrogen
_____ atoms of Oxygen
_____ atoms of Sulfur
_____ molecule/moles of NH4NO3
_____ molecule/moles of H2S

12. Let’s Step It Up a Little
2NH4NO3 + 3H2S
__4___ atoms of Nitrogen
__14___ atoms of Hydrogen
__6___ atoms of Oxygen
__3___ atoms of Sulfur
__2___ molecule/moles of NH4NO3
__3___ molecule/moles of H2S

13. You Must Be Joking! 2Na2CO3 + 3CO2 + 4NaCl + Mg(NO3)2
_____ atoms of Sodium
_____ atoms of Carbon
_____ atoms of Oxygen
_____ atoms of Chlorine
_____ atoms of Nitrogen
_____ atoms of Magnesium
_____molecules/moles of Na2CO3
_____ molecule/moles of CO2
_____ molecule/moles of NaCl
_____ molecule/moles of Mg(NO3)2

14. You Must Be Joking! 2Na2CO3 + 3CO2 + 4NaCl + Mg(NO3)2
__8___ atoms of Sodium
__5___ atoms of Carbon
__18___ atoms of Oxygen
__4___ atoms of Chlorine
__2___ atoms of Nitrogen
__1___ atom of Magnesium
__2___molecules/moles of Na2CO3
__3___ molecule/moles of CO2
__4___ molecule/moles of NaCl
__1___ molecule/moles of Mg(NO3)2

15. ® O + C O C O O C + O2 ® CO2 This equation is already balanced
What if it isn’t already?

16. ® O + C C O O C + O2 ® CO We need one more oxygen in the products.
Can’t change the formula, because it describes what is produced.
Remember, oxygen is a diatomic molecule.

17. ® C O O + C O C O The other Oxygen must be used to make another CO
But where did the other C come from?

18. C C O O + O C C O
Must have started with two C
2 C + O2 ® 2 CO

19. Rules for balancing
Write the correct formulas for all the reactants and products
Count the number of atoms of each type appearing on both sides
Balance the elements (make them same amount on reactant and product sides) one at a time by adding coefficients (the numbers in front).
Check to make sure it is balanced.

20. Never! Change a subscript to balance an equation.
If you change the formula you are describing a different reaction.
H2O is a different compound than H2O2
Never put a coefficient in the middle of a formula
2 NaCl is okay, Na2Cl is not.

21. Example
H2 + O2
H2O
Make a table to keep track of where you
are at

22. Example
H2 + O2
H2O R P 2 H 2 2 O 1
Need twice as much O in the product

23. Example
H2 + O2 2
H2O R P 2 H 2 2 O 1
Changes the O

24. Example
H2 + O2 2
H2O R P 2 H 2 2 O 1 2
Also changes the H

25. Example
H2 + O2 2
H2O R P 2 H 2 4 2 O 1 2
Need twice as much H in the reactant

26. Example 2
H2 + O2 2
H2O R P 2 H 2 4 2 O 1 2
Recount

27. Example 2
H2 + O2 2
H2O R P 4 2 H 2 4 2 O 1 2
The equation is balanced, has the same
number of each kind of atom on both sides

28. Example R P 4 2 H 2 4 2 O 1 2 2 H2 + O2 ® 2 H2O This is the answer
Not this

29. Examples CH4 + O2 ® CO2 + H2O AgNO3 + Cu ® Cu(NO3)2 + Ag
Mg + N2 ® Mg3N2
P + O2 ® P4O10
Na + H2O ® H2 + NaOH

30. Examples CH4 + 2O2 ® CO2 + 2H2O 2AgNO3 + Cu ® Cu(NO3)2 + 2Ag
3Mg + N2 ® Mg3N2
4P + 5O2 ® P4O10
2Na + 2H2O ® H2 + 2NaOH