1. Writing and Balancing Chemical Reactions

2. Like an equation in Math ::: 2+3=5
Chemical Equation
A description of a chemical reaction, using symbols and formulas to represent the elements and compounds involved
Like an equation in Math ::: 2+3=5

3. + : indicates that A and X react together
A chemical equation includes all substances involved in the reaction and all products that are formed.
A + X  AX
+ : indicates that A and X react together
 : read as “yields” points to the result of the reaction

4. A and X are the reactants
A + X  AX
The starting substances in the reaction are called the reactants and are left of the .
A and X are the reactants
The substances that are formed are called the products.
AX is the product
The products are to the right of the .

5. When writing a chemical equation it is important to know the physical form of the products and reactants.
The symbols are:
(g) = gas
(l) = liquid
(s) = solid
(aq) = aqueous solution (water)

6. The symbols are written
directly after the substance
you are describing.
A(s) + X(g)  AX(g)
If heat is needed to move a reaction, the Greek letter delta (Δ) is used above the yield arrow. Δ

7. We can interpret a chemical equation in several ways
EX. C(s) + O2(g)  CO2(g)
Qualitatively
Solid C and gaseous O2 react to form gaseous CO2
Microscopic Representation
One C atom reacts with one O molecule to form one molecule of CO2
Macroscopic Representation
One mole of C reacts with 1 mole of O gas to produce one mole of CO2

8. Not all reactions are this simple.
H2(g) + O2(g)  H2O(l)
This equation as it is written does not conform to the law of conservation of mass.
There 2 atoms of oxygen in the reactants ; but only one atom in the products!!
atoms cannot be created or destroyed
We need to balance this equation so it will agree with the law of conservation of mass

9. 4 H atoms + 2 O atoms  4 H atoms and 2 O atoms
We can use STOICHIOMETRIC COEFFICIENTS to adjust the ratio of the products and reactants.
H2(g) O2(g)  H2O(l)
2H2(g) O2(g)  2H2O(l)
4 H atoms + 2 O atoms  4 H atoms and 2 O atoms

10. We can only balance equations by adjusting coefficients
We cannot change subscripts
H2O to H2O2 X
We cannot add a reactant or product
H2 + O2  H2O + O X
Yes, the reaction looks balanced, but it no longer describes the desired reaction.

11. Balancing Chemical Equations
1. LEARN THESE DIATOMIC MOLECULES: O2 H2 N2 F2 Cl2 Br2 I2
2. Do NOT change the chemical formulas of the reactants or products (subscripts).
3. Start with the most complicated molecule and proceed element by element to determine coefficients. Save simplest molecule for last, particularly single element molecules.
4. Check equation by counting the number of each type of atom in reactants and products, making sure there is the same number on each side of the arrow.

12. MINOH
Metals, Ions, nonmetals, oxygen, hydrogen

13. Practice

14. Balancing Equations 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

15. What is a chemical equation?

16. A description of a chemical reaction, using symbols and formulas to represent the elements and compounds involved

17. What does the symbol Delta (Δ) mean when it is above the yield arrow?

18. Heat is needed

19. It is important to know the ________ form of the products and reactants in a chemical equation.

20. Physical

21. Balance the following equation:
H2(g) + O2(g)  H2O(l)

22. 2H2(g) + O2(g)  2H2O(l)

23. We can only balance equations by . . .

24. adjusting coefficients

25. 4Fe(s) + 3O2(g) ---> 2Fe2O3(g) Name the Reactants and the Products

26. 4Fe(s) and 3O2(g) = reactants
2Fe2O3(g) = products

27. Chemical equations must conform to the . . .

28. Law of Conservation of Mass

29. Balance the following equation:
Zn (s) + AgNO3 (aq)  Zn(NO3)2 (aq) + Ag (s)

30. Zn(s) + 2AgNO3(aq)  Zn(NO3)2(aq) + 2Ag (s)

31. To balance an equation you cannot add . . .

32. Reactants, Products or subscripts

33. Balance the following equation:
N2 (g) + H2 (g)  NH3 (g)

34. N2 (g) + 3H2 (g)  2NH3 (g)

35. Balance the following equation:
N2 (g) + O2 (g)  N2O5 (g)

36. 2N2 (g) + 5O2 (g)  2N2O5 (g)

37. Balance the following equation:
Ca (s) + H2O (l)  Ca(OH)2 (aq) + H2 (g)

38. Ca (s) + 2H2O (l)  Ca(OH)2 (aq) + H2 (g)

39. Balance the following equation: K (s) + H2O (l)  KOH (aq) + H2 (g)

40. 2K (s) + 2H2O (l)  2KOH (aq) + H2 (g)

41. Balance the following equation:
Zn (s) + S8 (s)  ZnS (s)

42. 8Zn (s) + S8 (s)  8ZnS (s)

43. Balance the following equation: C5H12 (l) + O2 (g)  H2O (g) + CO2 (g)

44. C5H12 (l) + 8O2 (g)  6H2O (g) + 5CO2 (g)