1. Chemical Equations and Reactions

2. Describing Chemical Changes or Reactions
Chemical Reaction: process by which one or more substances are changed into one or more different substances.
Original Substances  Resulting Substances
Reactants  Products

3. Evidence of a Chemical Reaction:
Easily observed changes that indicate a chemical reaction has occurred
Evolution of heat and light
Production of a gas
Formation of a precipitate
Color Change
Difficult to reverse

4. Word Equations
Write a word equation to describe the reaction of methane (natural gas) as it burns in the air to produce carbon dioxide and water vapor.
Methane + oxygen  carbon dioxide + water

5. Representing a Chemical Change
Chemical Equation: represents with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction.

6. Chemical Equation
Law of Conservation of Mass must be taken into account.
Adjust equation so that the same type of atoms and numbers of atoms are the same on both sides of the equation.
CH4(g) + O2(g)  CO2(g) + H2O(g)
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Symbols used in chemical equations, see p (s) solid, (l) liquid, (g) gas, (aq) aqueous, Δ heat
Notice (aq) refers to a solution in water and thus to a homogeneous mixture not a pure substance

7. Write a word & chemical equation
Solid sodium oxide is added to water (at room temp.) and forms sodium hydroxide which is dissolved in water.
Sodium oxide(s) + water(l)  sodium hydroxide (aq)
Na2O(s) + H2O(l)  NaOH(aq)
Na2O(s) + H2O(l)  2NaOH(aq)

8. Write a word & chemical equation
Hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water.
Hydrogen peroxide  oxygen + water
H2O2(aq)  O2(g) + H2O(l)
2H2O2(aq)  O2(g) + 2H2O(l)

9. Write a word & chemical equation
Solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper(II) nitrate.
Copper(s) + silver nitrate(aq)  silver(s) copper(II)nitrate(aq)
Cu(s) + AgNO3 (aq)  Ag (s) + Cu(NO3)2 (aq)
Cu(s) + 2AgNO3(aq)  2Ag (s) + Cu(NO3)2 (aq)

10. Write a word & balanced chemical equation
Solid zinc metal reacts with aqueous copper(II) sulfate to produce solid copper metal and aqueous zinc sulfate.
Zinc(s) + copper(II)sulfate(aq)copper (s) zinc sulfate (aq)
Zn(s) + CuSO4 (aq) Cu(s) + ZnSO4(aq)

11. Guidelines for Balancing Equations
Write the chemical equation with the correct formulas for the reactants and products.
Count the number and types of atoms on both sides of the equation.
Balance the atoms of the elements that appear only once on each side of the equation.

12. Balancing Equations
Balance polyatomic ions that appear on each side of the equation.
Balance hydrogen and oxygen after all other atoms have been balanced.
Check both sides – count each element.
Use lowest coefficients.

13. HOFBrINCl What’s it spell? Hydrogen Oxygen Fluorine Bromine Iodine
Nitrogen
Chlorine
HOFBrINCl

14. HOFBrINCl Elements that exist as diatomic molecules.
Cl2 is electrically neutral, whereas in a compound such as NaCl, chlorine is the chloride ion with a negative charge.

15. Write a Balanced Chemical Equation:
Zinc(s) + hydrochloric acid(aq) zinc chloride (aq) and hydrogen gas.
Zn(s) + HCl (aq)  ZnCl2(aq) + H2(g)
Zn(s) + 2 HCl(aq)  ZnCl2(aq) + H2(g)

16. Write a Balanced Chemical Equation:
Aluminum carbide, Al4C3(s) + watermethane gas, CH4 + aluminum hydroxide(s)
Al4C3 (s) + H2O(l)  CH4(g) + Al(OH)3(s)
Al4C3(s) + 12 H2O(l) 3CH4(g) Al(OH)3(s)

17. Write a Balanced Chemical Equation:
Aluminum sulfate + calcium hydroxide aluminum hydroxide calcium sulfate
Al2(SO4)3 + Ca(OH)2 Al(OH) CaSO4
Al2(SO4)3 +3Ca(OH)2 2Al(OH) CaSO4

18. CHO method: Combustion Reactions
Combustion Reaction contains a hydrocarbon + oxygen to yield carbon dioxide and water.
Balance carbon first, then hydrogen and finally oxygen.
C2H6 + O2  CO2 + H2O
2C2H6 +7 O2 4 CO2 + 6H2O

19. Types of Chemical Reactions
Five Basic Types of Chemical Reactions:
Synthesis
Decomposition
Single-displacement
Double-displacement
Combustion

20. Synthesis Two or more substances combine to form a new compound.
A + B  AB
(A & B may be compounds or elements)

21. Synthesis Reactions Here is an example

22. Synthesis Examples Mg(s) + O2(g)  MgO(s) 2Mg(s) + O2(g) 2MgO(s)
Ba (s) + S8 (s)  BaS(s)
8Ba (s) + S8 (s)  8 BaS(s)
Na(s) + Cl2(g)  NaCl
2 Na(s) + Cl2 (g)  2NaCl

23. Basic Oxides Metal oxides react with water to produce Bases
e.g. Na2O + H2O → 2NaOH
K2O +H2O  2KOH
CaO +H2O  Ca(OH)2

24. Acidic oxides
Non-metal oxides react with water in a synthesis reaction to produce oxy-acids
e.g. SO2 +H2O  H2SO3 sulphurous acid
SO3 +H2O  H2SO4 sulphuric acid
NO2 +H2O  HNO3 nitric acid
CO2 +H2O  H2CO3 carbonic acid
P4O10 +H2O  H3PO4 phosphoric acid
B2O3 +3H2O  2H3BO3 boric acid

25. Acidic oxide and basic oxide together!
When an acidic oxide (ie nonmetal oxide) reacts with a basic oxide (ie metal oxide) the result is a salt with a polyatomic ion
Li2O + CO2 → lithium carbonate
Li2O + CO2 → Li2CO3

26. Synthesis reactions- overview
A- elmt +elmt = Cmpd
2Na + Cl2= 2NaCl
B- water + NMO(acidic oxide) =Acid
H2O + CO2= H2CO3
C- water + MO (basic oxide) = Base
H2O + Li2O= 2 LiOH
D- MO + NMO= Salt with polyatomic
Li2O + CO2= Li2CO3

27. Decompositon
A single compound undergoes a reaction that produces 2 or more simpler substances.
AB  A + B
(A & B can be elements or compounds)

28. Decomposition Reactions
Another view of a decomposition reaction:

29. Decomposition Examples
H20 (l)  H2 (g) + O2 (g)
2H20 (l)  2H2 (g) + O2 (g)
HgO (s)  Hg (g) + O2 (g)
2HgO (s)  2Hg (g) + O2 (g)
CaCO3 (s)  CaO (s) + CO2 (g)

30. Decomposition Exceptions
Carbonates and bicarbonates are special case decomposition reactions that do not go to the elements.
Carbonates (CO32-) decompose to carbon dioxide and a metal oxide
Example: CaCO3  CO2 + CaO
Hydrogen Carbonates (HCO3-) decompose to carbon dioxide, water and a metal oxide
Example: Ca(HCO3)2  2CO2 + H2O + CaO

31. Decomposition reactions- opposites of synthesis
A- Cmpd = elmt +elmt
2NaCl = 2Na + Cl2
B- Acid = water + NMO(acidic oxide)
H2CO3 = H2O + CO2
C- Base = water + MO (basic oxide)
2LiOH = H2O + Li2O
D- Salt with polyatomic = MO + NMO
Li2CO3 = Li2O + CO2

32. Single Displacement Reactions
One element replaces a similar element in a compound.
A + BC  AC + B where A and B are metals and C is a non-metal or
A + BC  BA + C where A and C are non- metals and B is a metal

33. Single Displacement Reactions
Another view:

34. Single Displacement Examples
2Al(s) + 3Pb(NO3)2 (aq)  3Pb(s) + 2Al(NO3)3 (aq)
Al replaces Pb (2 metal ions change position)
Cl2(g) + 2 KBr(aq)  2KCl(aq) + Br2(g)
Cl replaces Br (2 non-metal ions change position)

35. Activity Series
The ability of an element to react is called the elements “activity.”
The more readily an element reacts – the greater “activity” it has.

36. : Activity Series
A list organized by the ease at which certain elements will undergo a chemical reaction.(p.89)
Li K Ba Ca Na Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au
The H near the end represents H of acid and NOT H of water
Notice all the metals used in jewelry are on the far right side
The order is determined by single-displacement reactions.
The list on p.165, the first 5 react with water (HOH) and the ones up to H react with acid (first 12)

37. Activity Series
Most Active
Least Active
The most active element is placed at the top (or on the left) and can replace each of the elements below it. (or to the right)
Most active
Least active

38. An element further down the list can only replace an element below it –not above it.
The Activity Series will predict whether or not a reaction will take place.

39. Activity series of metals
lithium
potassium
barium
calcium
sodium
Activity series of metals
React vigorously with cold water 
React slowly with cold water
magnesium
aluminum
zinc
iron
React very slowly with steam
but are quite reactive in acid
increasing reactivity
nickel
Tin
Lead
React moderately with acid
copper
mercury
silver
gold
Unreactive in acid

40. Activity series of metals used to predict reactions
lithium
potassium
barium
calcium
sodium
Activity series of metals used to predict reactions
1. Will potassium react with sodium iodide?
Yes/No???
magnesium
aluminum
zinc
iron
2. Will calcium react with copper selenide?
Yes/No???
increasing reactivity
3. Will sodium iodide react with potassium?
Yes/No??? Should be same answer as 1
nickel
Tin
Lead
4. Will zinc chloride react with iron?
Yes/No???
5. Will zinc chloride react with water?
copper
mercury
silver
gold
Yes/No???
6. Will zinc chloride react with an acid?
Yes/No???

41. Halogen activity series
For the halogens in a single displacement reaction the order is fluorine (on top) most reactive followed by Cl, Br, I, At (least reactive) just as the order in column 17 of the periodic table
Thus, F can replace I but not the other way around

42. Activity Series Examples
Al will replace Zn:
2Al (s) + 3ZnCl2(aq)  3Zn(s) + 2AlCl3 (aq)
Co will not replace Na
Co(s) + NaCl(aq)  no rxn.
Cl will replace Br
Cl2 + NaBr Br2 + NaCl
Cl will not replace F
NaF + Cl2  no rxn

43. Double Displacement Reactions
The ions of two compounds exchange places in an aqueous solution to form two new compounds.
A double displacement reaction is likely to occur if on the product side there is the formation of a liquid (as in water), a gas (CO2, SO2, SH2, NH3), or a solid (a precipitate insoluble i.e (s) for solid…see charts)
AB + CD  AD + CB

44. Double Displacement Examples
2KI(aq) + Pb(NO3)2(aq)  2 KNO3(aq) + PbI2 (s)
K cation replaces Pb cation
I anion replaces nitrate anion
FeS(s) + 2HCl(aq)  H2S(g) + FeCl2(aq)
Fe cation replaces H cation
S anion replaces Cl anion

45. …but there is more!!
Double displacement reactions only occur if at least one product is a solid, liquid or a gas! Like: CO2(g), H2O (l), NH3(g), SO2(g), PbSO4(s), H2S (g)
Not like ______ (aq) + _____ (aq)
If both products are aqueous, then no reaction occurs!!
Check your solubility rules! Write in the state of your previous products
If the products H2CO3, H2SO3, NH4OH are produced in a double displacement reaction, they further break down and form a gas and water.

46. H2CO3 breaks down into CO2(g) and H2O(l)
H2SO3 breaks down into SO2(g) and H2O(l)
NH4OH breaks down into NH3(g) and H2O(l)
Example:
Na2SO3(aq) + 2HCl(aq)  2NaCl(aq) + H2SO3(aq)
Na2SO3(aq)+2HCl(aq) 2NaCl(aq) +H2O(l) + SO2(g)

47. Some simple solubility rules
All acids and alkali metal salts and NH4+ salts are soluble
All nitrate and acetate salts are soluble.
All chlorides are soluble except AgCl and Hg2Cl2 PbCl2
All sulfates are soluble except PbSO4, Hg2SO4, SrSO4, BaSO4. Ag2SO4 and CaSO4.
All sulfides are insoluble except those of the Group IA (1), IIA (2) and ammonium sulfide.
All hydroxides are insoluble except those of the group IA(1) and Ba(OH)2. Sr(OH)2 and Ca(OH)2 are slightly soluble.

48. Reading the solubility chart
If a compound is soluble…it dissolves in water then you can write (aq) after the formula if water is present.
If a compound is insoluble (not soluble) then you can write (s) after the formula since it does not dissolve.

49. Mixed Practice
State the type, predict the products, and balance the following reactions:
BaCl2 + H2SO4 
Zn + CuSO4 
Cs + Br2 
FeCO3 
C3H8 + O2 

50. Mixed Practice
State the type, predict the products, and balance the following reactions:
BaCl2 + H2SO4  2HCl +BaSO4
Zn + CuSO4  Cu + ZnSO4
2Cs + Br2  2CsBr
CS2  C + 2S
C3H8 + 5O2  3CO2 + 4H20

51. Practice makes perfect
Try we, ce, bce p.155
Try synthesis/decomposition reactions
p. 161
Try single/double displacement reactions
p. 169
p.177