1. Chemical Reactions

2. Objectives- Describing Chemical Reactions
Describe how to write a word equation.
Describe how to write a skeleton equation.
Describe the steps for writing a balanced chemical equation.

3. Word Equations These word equations are exactly as they sound.
To write a word equation, we write the names of the reactants to the left of the arrow separated by plus signs.
On the right we write the products, also separated by plus signs.

4. Examples H2 + O2  H2O Fe + O2  Fe2O3 H2O2  H2O + O2
Hydrogen + Oxygen  Water
Fe + O2  Fe2O3
Iron + Oxygen  Iron(III) Oxide
H2O2  H2O + O2
Hydrogen Peroxide  Water + Oxygen

5. Chemical Equations
A chemical equation is a representation of a chemical reaction, with reactants on the left of the arrow, and products on the right.
We should already be aware of what a chemical equation is, but a subsect of these equations is known as a skeleton equation.
A skeleton equation is one where the formulas of the reactants and products are listed but no amounts are shown. (sometimes called unbalanced equations)

6. Common Symbols “+” used to separate two reactants/products
“” a way to show reactants that “yield” a product
“⇌” used in the case of a reversible reaction
(s) used for a solid substance
(l) designates a substance in the liquid state
(g) designates a substance in the gaseous state
(aq) designates an aqueous solution, or one dissolved in water

7. Balancing Chemical Equations (Refresher)
H2 + O2  H2O
Al2O3  Al + O2
S8 + O2  SO2
P4 + O2  P2O5
Cr + O2  Cr2O3

8. Objectives- Types of Chemical Reactions
Describe the five general types of reactions.
Predict the products of the five general types of reactions.

9. Classifying Chemical Reactions
Five types of reactions
Synthesis (Combination)
Decomposition
Single Replacement
Double Replacement
Combustion

10. Synthesis Reactions (Combination)
Two or more compounds react to form a single product
Identifying characteristic: SINGLE PRODUCT
General form
A + B  AB
2 Na + Cl2  2 NaCl
4 Fe + 3 O2  2 Fe2O3
CO2 + H2O  H2CO3

11. An analogy:
Two single people go to a dance and leave as couple

12. Decomposition
Single compound breaks down into two or more simpler substances
Identifying characteristic: ONE REACTANT
General format
AB  A + B
2 H2O  2 H2 + O2
CaCO3  CaO + CO2

13. An analogy:
A couple breaks up…

14. Single-Replacement Reactions
One substance replaces another similar substance (like replaces like)
Identifying characteristic: REACTANTS are always 1 ELEMENT & 1 COMPOUND.
General form: A + BX  AX + B
2Al + 3CuCl2  2AlCl3 + 3Cu
Fe + Ni(NO3)2  Fe(NO3)2 + Ni
Cl2 + 2 KI  2 KCl + I2

15. During a dance, someone cuts in
An analogy:
During a dance, someone cuts in
Remember metal replaces metal

16. The Activity Series of Metals & Single Replacement Reactions
Not all metals have the ability to replace another metal in a compound
Must use the “Activity Series of Metals” to determine if a single replacement reaction will occur

17. Activity Series of Metals
Metals cont’d. Li Cd K Co Ba Ni Sr Sn Ca Pb Na H Mg Cu Al Ag Mn Hg Zn Au Fe
Metals from Li to Na will replace H from acids and water.
Metals from Mg to Pb will replace H from acids only.
Decreasing Activity

18. If an element is higher on the activity series it will replace the other. This means the reaction will occur.
Li NaCl 
Na LiCl
Ca BaSO4 
No reaction
Cu AgNO3 
CuNO Ag

19. Double-Replacement Reactions
Identifying characteristic: presence of 2 COMPOUNDS AS REACTANTS, and the switching of two cations between compounds.
General form:
AX(aq) + BY(aq)  AY + BX
K2CO3(aq) + BaCl2(aq)  KCl(aq) + BaCO3(s)
NaCl(aq) + AgNO3(aq)  NaNO3(aq) + AgCl(s)

20. An analogy:
Two couples swap partners

21. Double-Replacement Reactions (cont)
Not all double replacement reactions will occur. This depends on the solubility rules which we will discuss later.
For now assume they occur when writing or balancing equations

22. Combustion Reactions
Oxygen and a carbon/hydrogen compound are reactants
Identifying characteristic: have 2 PRODUCTS; CO2 & H2O.
General form:
CxHy + O2  CO2 + H2O
C2H5OH + O2  2 CO H2O
C3H8 + 5 O2  3 CO2 + 4 H2O

23. Review of General Forms for Reactions
The five types of reactions have the following general forms:
A + B  AB (synthesis)
AB  A + B (decomposition)
A + BX  AX + B (single)
AX + BY  AY + BX (double)
CnHm + O2  CO2 + H2O (combustion)

24. Answer the following questions:
1. Name the five main types of reactions.
2. What is the identifying characteristic of a synthesis reaction?
3. What is the identifying characteristic of a decomposition reaction?

25. What are the substances on the left side of a chemical reaction called?
5. What is the activity series used for?
6. What are the products of a combustion reaction?

26. Name That Rxn Type! 2H2O2  2H2O + O2 2Cu + O2  2CuO
Zn + 2AgNO3  Zn(NO3)2 + 2Ag
4NaCl + 2H2SO4  2Na2SO4 + 4HCl
2C2H2 + 3O2  2CO2 + 2H2O

27. Balancing Equations Reminders
All chemical equations must be balanced
All reactants and products must be correctly written (i.e., correct formulas!)
ID reaction type & predict products
Coefficients may be added to satisfy Law of Conservation of Matter
NEVER CHANGE A CORRECT SUBSCRIPT !!!!!!!!!!!!!!!!

28. Balancing Equations Reminders(cont)
Never automatically bring subscripts from reactant side to product side
Remember diatomic elements!!!
H2, N2, O2 and the halogens (Group 7A)
Use pencil and check your work!

29. Predicting Products Use Activity Series for SR rxns.
If the rxn will not proceed:
Put a diagonal line through the arrow
Or write NR after the arrow
For double replacement reactions you will need to use the solubility rules to determine if the reaction will occur.

30. Phase Indicators
Tells the phase of the reactants and products in a chemical equation
Solid (s) [formation of a solid]
Ca3(PO4)2(s)
Liquid (l) [formation of a liquid]
HOH(l) - same as –H2O(l)
Gas (g) [formation of a gas]
H2(g), CO2(g), O2(g)
Aqueous (aq) [dissolved ions]
NaCl(aq)

31. Solubility Definitions
Soluble
Can Dissolve in Water
Aqueous is the phase indicator (aq)
Slightly Soluble
Only a insignificant amount dissolves
Solid the phase indicator (s)
Insoluble
Does not Dissolve
On the next slide is a table of solubilities. What trends do you notice?

33. Solubility Rules
The previous table is time consuming to remember and use. Although you do not need to memorize we will instead use “Solubility Rules” located with your periodic table.

34. Question: The solubility rules are mostly based on the anion or cation
Question: The solubility rules are mostly based on the anion or cation? (Which one do you look at in order to determine which rule to use?)

35. Identify the following as SOLUBLE or INSOLUBLE
Identify the following as SOLUBLE or INSOLUBLE. Write the correct phase indicator.
NaNO3 NaCl CaCrO4
BaSO4 BaS (NH4)2CO3
AgNO3 K2CrO4 Ca(OH)2
See wksht:

36. Implications for DR Reactions
A reaction takes place when:
A new substance forms
Solids, liquids, or gases
No reaction takes place when:
Only soluble ions exist
Aqueous

37. Double Replacement Rxns
Reactants must always be dissolved in water; i.e., phase subscript = (aq)
Always write formulas for products (predict products)
Use solubility rules to determine if at least one of the products will be a solid, liquid or gas--NOT AQUEOUS
If both products are (aq), no reaction takes place
Put a diagonal line through the arrow or
Write NR over the arrow

38. Practice SO NO REACTION AgNO3(aq) + Na2S(aq)  Ag2S(s) + NaNO3(aq)
2KNO3(aq) + Na2S(aq) 
K2S(aq) +2NaNO3(aq)
SO NO REACTION
NaOH(aq) + Pb(NO3)(aq) 
NaNO3(aq) + Pb(OH)2(aq)
NaOH(aq) + KNO3(aq)  NR

39. Law of Conservation of Mass
Matter cannot be created or destroyed, it may be recombined to form new substances
Starting mass must equal ending mass
Starting # of atoms must equal ending # of atoms

40. Evidence of a Reaction New substance forms Change in Temperature
Precipitate (solids falls from a solution)
Gas (bubbles…)
Water (neutralization [acid/base] reaction)
Change in Temperature
Exothermic or Endothermic
Transfer of Electrons
“Oxidation-Reduction” Reaction

41. Objectives- Reaction in Aqueous Solutions
Describe the information found in a net ionic equation.
Predict the formation of a precipitate in a double replacement reaction.

42. Net Ionic Equations First lets look at the following reaction:
AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
If we separate all the pieces involved in this reaction we would arrive at the following:
Ag+ (aq) + NO3-1 (aq) + Na+(aq) + Cl-1 (aq) 
AgCl (s) + Na+1 (aq) + NO3-1 (aq)
What looks out of place with this equation?

43. Net Ionic Equations
Our next step is to cancel out anything that appears on each side PERFECTLY.
Ag+ (aq) + NO3-1 (aq) + Na+(aq) + Cl-1 (aq) 
AgCl (s) + Na+1 (aq) + NO3-1 (aq)
That what we have canceled out is known as a spectator ion, something that does not directly involved in the reaction.
What are we left with?
This is called the net ionic equation, this shows only those particles that are directly involved in a chemical change.

44. Balancing the Net Ionic EQ
Pb(s) + AgNO3 (aq)  Ag(s) + Pb(NO3)2 (aq)
Let’s work through this one together.

45. Predicting the Formation of a Precipitate
We can predict the formation of a precipitate by using the general rules of solubility.

46. Predicting the Formation of a Precipitate
Looking at the list of soluble and insoluble compounds we should be able to predict the possible products from the following reaction.
2Na+ (aq) + CO32- (aq) + Ba+2 (aq) + 2NO3-1 (aq)  ?