1. Introduction
Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken
Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes.
Symbols represent elements, formulas describe compounds, chemical equations describe a chemical reaction

2. Chemical Equations
Lavoisier, 1788
Because of the principle of the conservation of matter,
an equation must be balanced.
It must have the same number of atoms of the same kind on both sides.

3. Scientists know that there must be the same number of atoms on each side of the arrow.

4. To balance the chemical equation, you must add COEFFICIENTS to the different parts of the equation.

5. Step # 1
Determine the number of atoms for each element.

6. Determine the number of atoms for each element.
Mg O MgO

7. Determine the number of atoms for each element.
Mg O MgO
1 Magnesium Magnesium
2 Oxygen 1 Oxygen

8. Try to add coefficients to the equation to get the same number of atoms on each side.
Mg O MgO
1 Magnesium Magnesium
2 Oxygen 1 Oxygen 2

9. Recount the atoms after adding a coefficient.
Mg O MgO
1 Magnesium Magnesium
2 Oxygen 2 Oxygen
Still out of balance… 2

10. Add a coefficient to the other side
Mg O MgO
1 Magnesium Magnesium
2 Oxygen 2 Oxygen
Recount again… 2 2

11. Recount the atoms… Mg + O2 MgO 2 2 2 Magnesium 2 Magnesium
2 Oxygen 2 Oxygen
It’s balanced!!! 2

12. Try these…
Ca O CaO

13. Count atoms… Ca + O2 CaO calcium 1 calcium 1 oxygen 2 oxygen 1
not in balance – so…

14. Add coefficients… then recount atoms2
Ca O CaO
calcium 2 calcium 2
oxygen oxygen 2
Now it’s balanced 2

15. What type of reaction is this?
Synthesis
Decomposition
Single replacement
Double replacement
Combustion

16. synthesis

17. #3 Try this one on your own
H2O H2O O2

18. #3 counting atoms H2O2 H2O + O2 hydrogen 2 hydrogen 2
oxygen oxygen 3

19. #3 adding coefficients and recount2
H2O H2O O2
hydrogen hydrogen 4
oxygen oxygen 4 2

20. What type of reaction?
decomposition

21. #4 counting atoms N2 + H2 NH3 nitrogen 2 nitrogen 1
hydrogen hydrogen 3

22. #4 adding coefficients N2 + H2 NH3 2 4 nitrogen 2 4 nitrogen 1 4
hydrogen hydrogen
Still out of balance…. 2 4

23. #4 adding more coefficients
N H NH3
nitrogen nitrogen 1 2
hydrogen hydrogen
Sometimes you have to be creative …. 6 2

24. What type of reaction?
synthesis

25. #5 try this one on your own
Cu2O C Cu CO2
copper copper
oxygen oxygen
carbon carbon

26. #5 counting atoms Cu2O + C Cu + CO2 copper 2 copper 1
oxygen oxygen 2
carbon carbon 1

27. #5 adding coefficients Cu2O + C Cu + CO2 2 copper 2 4 copper 1
oxygen oxygen 2
carbon carbon 1 2

28. #5 still adding coefficients
Cu2O C Cu CO2
copper copper
oxygen oxygen 2
carbon carbon 1 2 4

29. What type of reaction is this?
Single replacement

30. Problems 1-7 on the back Remember, count the atoms first
Add coefficients to balance one of the atoms first
Recount atoms
Keep working the coefficients until atoms are balanced

31. Problems Na + MgF2 NaF + Mg Mg + HCl MgCl2 + H2 Cl2 + KI KCl + I2
NaCl Na + Cl2
Na + O Na2O
Na + HCl H2 + NaCl
K + Cl KCl
CHALLENGE!!
CO H2O C6H12O6 + O2

32. Solutions 2 Na + MgF2 2 NaF + Mg 2 Mg + 4 HCl 2 MgCl2 + 2 H2
Cl2 + 2KI KCl + I2
2 NaCl Na + Cl2
4 Na + O Na2O
2 Na + 2 HCl H NaCl
2 K + Cl KCl

33. Challenge solution
6 CO H2O C6H12O O2