1. CHEMICAL REACTIONS

2. SO FAR . . .
So far we have looked at the properties of individual atoms and molecules
Atomic number
Atomic mass
Ions
Lewis dot structures
Molecular shapes
Naming
Moles

3. HOW DO THESE ATOMS AND MOLECULES INTERACT?
The way that these atoms and molecules interact with each other is through chemical reactions
Chemical reaction: Change of one or more substances into a different substance.

4. BEFORE WE BEGIN Important concept (by Antoine Lavosier):
Conservation of mass: Matter is neither created or destroyed in a chemical reaction
In other words, you must have the same components in the beginning and end of a chemical reaction

5. Catalysis
Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst

6. GENERAL TYPES OF REACTIONS
Gas evolution reactions: these are reactions that occur in liquids and produce a gaseous product
For example – Alka Seltzer in H2O
Oxidation-reduction reactions: electrons are transferred from one substance to another
For example – rust formation, batteries

7. GENERAL TYPES OF REACTIONS
Precipitation reactions: reactions that occur in liquid that produce a solid substance
Acid Base Neutralization: an acid will lose a H+ ion (a proton) and a base is a substance which can accept a proton.
When equal amounts of an acid and base
react, they neutralize each other

8. HOW DO WE KNOW THAT A CHEMICAL REACTION HAS TAKEN PLACE?
Many chemical reactions produce easily detectable changes
Color change
Formation of a solid
Formation of a gas
Heat absorption or emission (uses up or produces heat)
Light absorption or emission

9. HOW DO WE KNOW THAT A CHEMICAL REACTION HAS TAKEN PLACE?
The previous are only INDICATIONS of a chemical reaction
Chemical analysis is needed to verify if a reaction is actually occurring.
For example: Boiling water looks like a gas is being produced, but this is a physical change, NOT A CHEMICAL CHANGE
H2O(l)  H2O(g) NO NEW SUBSTANCE

10. SHOWING CHEMICAL REACTIONS
Chemical equations are a way that chemists summarize a chemical reaction that takes place
Reactions take the following general format
Reactants  Products
A set of chemicals react to form a set of products

11. REACTIONS AND ENERGY
Chemical reactions either absorb energy/heat from their surroundings or they release energy/heat:
EXOTHERMIC: a chemical reaction that produces heat (ie. Burning gas in your car)
ENDOTHERMIC: a chemical reaction that absorbs heat (ie. Icy hot)

12. SHOWING CHEMICAL REACTIONS
In chemical reactions, the state of matter is usually described:
Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)

13. PRACTICE
For each of the following, translate the sentence into a chemical reaction:
Solid zinc is mixed with aqueous hydrochloric acid to form zinc chloride and hydrogen gas
Aqueous sulfuric acid is combined with solid gold to produce aqueous gold(I) sulfate and hydrogen gas

14. ANSWER Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g)
H2SO4(aq) + Au  Au2SO4(aq) + H2(g)

15. HOW DO WE APPLY CONSERVATION OF MATTER TO CHEMICAL REACTIONS?
C3H8(l) + O2(g)  CO2(g) + H2O(l)
Let’s examine this reaction closer:
How many atoms of each element are on each side of the reaction?
Reactants Products
C C
H H
O O

16. SPECIFIC TYPES OF CHEMICAL REACTIONS
There are 5 specific types of chemical reactions.
Synthesis (combination) reactions
Decomposition reactions
Displacement reactions
Double displacement reactions
Combustion reactions (special)

17. SYNTHESIS REACTIONS
A synthesis reaction is when you take simpler molecules and combine them to form more complex molecules
They have the following general set up
A + B  AB
Example:
2Na(s) + Cl2(g)  2NaCl(aq)

18. DECOMPOSITION REACTIONS
These are the opposite of the synthesis reactions. A more complex compound breaks down to form simpler compounds.
They have the following general set up
AB  A + B
Example:
2H2O(l)  2H2(g) + O2(g)

19. DISPLACEMENT REACTIONS (SINGLE DISPLACEMENT)
One element displaces (or takes the place of) another element in a compound.
They have the following general set up
A + BC  AC + B
Example:
Zn(s) + CuCl2(aq)  ZnCl2(aq) + Cu(s)

20. DOUBLE DISPLACEMENT REACTION
Two elements, in separate compounds, displace (or switch places with) each other.
They have the following general set up
AB + CD  AD +BC
Example:
AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)

21. COMBUSTION REACTIONS
When a compound combines with oxygen to form carbon dioxide, water and heat
They have the following general set up
Molecule + O2  CO2 + H2O + heat
Example:
2C2H6 + 7O2  4CO2 + 6H2O + heat

22. TRY THESE
Translate, balance and tell what type of reactions the following are:
Chlorine gas combines with sodium bromide to form sodium chloride and bromine gas.
Mercury(II) oxide breaks apart to form mercury and oxygen gas.

23. ANSWER Cl2 + 2NaBr  Br2 + 2NaCl 2HgO  2Hg + O2
The chlorine displaces the bromine in sodium bromide
This is a SINGLE DISPLACEMENT reaction
2HgO  2Hg + O2
The mercury(II) oxide breaks apart into mercury and oxygen
This is a DECOMPOSITION reaction

24. GENERAL TYPES OF REACTIONS (EXPANDED)
Before we can describe the general types of reactions, in detail, we have to visit the concept of solubility
Soluble: the substance in question will dissolve in water
Insoluble: the substance in question will NOT dissolve in water

25. WHY SOLUBILITY
If you know what compounds are soluble, you can figure out if a reaction is:
Gas evolution reaction
Precipitation reaction
If soluble, the reaction will not form a precipitate or evolve a gas

26. SOLUBLE (VERY IMPORTANT – MAKE SURE YOU COPY)
All acetates (C2H3O2-) except Fe+3
All ammonium (NH4+) compounds
All bromides (Br-) except Ag+, Hg2+2, and Pb+2
All chlorates (ClO3-)
All chlorides (Cl-) except Ag+ and Pb+2

27. SOLUBLE (VERY IMPORTANT – MAKE SURE YOU COPY)
All iodides (I-) except Ag+, Hg2+2, and Pb+2
All nitrates (NO3-)
All perchlorates (ClO4-)
All sulfates (SO4-2) except Ca+2, Ba+2, Pb+2, Sr+2, Hg2+2

28. INSOLUBLE Insoluble Carbonates (CO3-2), except group 1 and NH4+
Chromates (CrO4-2), except group 1 and NH4+
Hydroxides (OH-), except group 1, Ca+2, Sr+2, and Ba+2
Oxalates (C2O4-2), except group 1 and NH4+

29. INSOLUBLE Oxides (O-2), except group 1, Ca+2, Sr+2, and Ba+2
Phosphates (PO4-3), except group 1 and NH4+
Sulfides (S-2), except those of group 1, group 2, and NH4+

30. SOLUBLE OR INSOLUBLE? H2SO4 Ca(C2H3O2)2 AgNO3 Na2O Li2CO3 BaC2O4
Mg(OH)2

31. ANSWER
Soluble
Insoluble

32. WHY DO WE CARE ABOUT SOLUBILITY?
By knowing the solubility rules, you will be able to do further analysis to determine if a chemical reaction will form a precipitate or evolve a gas
If a chemical does not precipitate out of solution or produce a gas (have the product insoluble), then the reaction will not be a gas evolution or precipitation reaction

33. Remember!
Soluble – dissolves in water. Does NOT form a solid (s) precipitate
Insoluble – does NOT dissolve in water. Forms a solid (s) precipitate

34. EXAMPLE
Examine the reactions below, determine which reaction produces a precipitate or not
Ba(OH)2 + K2O  BaO + 2KOH
(leave space in your notes)
2H3PO4 + 3BaO  Ba3(PO4)2 + 3H2O

35. ANSWER Ba(OH)2(aq) + K2O(aq)  BaO(aq) + 2KOH(aq)
BaO is soluble
KOH is soluble
Since both products are soluble, there is no precipitate
2H3PO4(aq) + 3BaO(aq)  Ba3(PO4)2(s) + 3H2O(l)
Ba3(PO4)2 is insoluble.
This means that as the reaction progresses, the Ba3(PO4)2 is a precipitate that is produced.

36. GENERAL TYPES OF REACTIONS (REVISITED)
Precipitation reactions
Only insoluble compounds form precipitates
If any product is insoluble, it forms a precipitate

37. PRECIPITATION REACTION
How to determine:
Write the two compounds in question as reactants
Na2CO3 + CuCl2 
Write the formulas of the potential products of the reaction
Na2CO3 + CuCl2 NaCl + CuCO3

38. PRECIPITATION REACTION
Look at the solubility rules to determine the solubility of the products
NaCl  soluble
CuCO3  insoluble
Write the equation with states of matter
Na2CO3(aq) + CuCl2(aq) NaCl(aq) + CuCO3(s)

39. PRECIPITATION REACTION
Balance the equation
Na2CO3(aq) + CuCl2(aq) 2NaCl(aq) + CuCO3(s)

40. GAS EVOLUTION REACTIONS
Whenever a reaction produces a gas, that gas will leave the reaction (bubble forms)
If a product is a gas, then you have a gas evolution reaction
HCl(aq) + NaHCO3(aq)  H2O(l) + NaCl(aq) + CO2(g)
This is the reaction of Alka Seltzer with your stomach acid

41. OXIDATION-REDUCTION REACTIONS
These reactions (redox) involve the transfer of electrons from one element to another
In order to understand these reactions better, we must look at the charges of the elements in a chemical reaction

42. DEFINITIONS
Oxidation: when an element loses electrons (the atom becomes +)
Reduction: when an element gains electrons (the atom becomes -)
Oxidation and reduction must occur together so the electrons can travel from one element to another

43. OXIDATION-REDUCTION REACTIONS
Example
4Na(s) + O2(g)  2Na2O
4 Na (s)  4 Na+ + 4e-
4e- + 2O  2O-2
In this example, Na goes from a neutral charge to a +1, it needed to lose an electron
O goes from a neutral charge to a -2, it had to gain electrons

44. TRY THESE
In each of the following reactions, identify the element that is oxidized and the element that is reduced:
2Na + Cl2  2NaCl
4Fe + 3O2  Fe2O3

45. ANSWER 2Na + Cl2  2NaCl 4Fe + 3O2  2Fe2O3
2Na  2Na+ + 2e- (oxidized)
2e- + 2Cl  2Cl- (reduced)
4Fe + 3O2  2Fe2O3
4Fe  4Fe e-
12e- + 6 O  6 O-2

46. SUMMARY There are 3 general types of reactions Precipitation
One of the products must be insoluble
Use the solubility rules
Gas evolution
If a gas is produced, it will come out of solution
Oxidation-reduction
Involves the movement of electrons
Something must be oxidized (lose electrons) and something must be reduced (gain electrons)

47. SUMMARY There are 5 specific types of reactions Synthesis
A + B  AB
Decomposition
AB  A + B
Displacement
A + BC  AB + C
Double displacement
AB + CD  AD + BC
Combustion

48. SUMMARY
With any sort of chemical reaction, we must follow the law of conservation of mass
Therefore, every chemical reaction must have the same number of atoms in the reactants and products
To balance, use the following tips

49. SUMMARY Write the skeletal reaction with just the compounds involved.
If an element occurs in only 1 compound on both sides of the reaction, balance it first. Otherwise, balance metals before nonmetals
Save diatomic molecules and/or water for last
If a balanced equation contains coefficient fractions, clear these by multiplying the entire equation by the appropriate number
Check to make sure the equation is balanced by summing the atoms on each side of the reaction