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
Colour Change

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. 77.

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? Bromine Iodine Nitrogen Chlorine Hydrogen
Oxygen
Fluorine
HOFBrINCl

14. BrINClHOF 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-replacement
Double-replacement
Combustion

20. Synthesis Two or more substances combine to form a new compound.
A + X  AX
(A & X 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. Basic Oxides Metal oxides react with water to produce Bases
e.g. Na2O + H2O → 2NaOH
K2O +H2O  2KOH
CaO +H2O  Ca(OH)2

25. 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 +H2O  H3BO3 boric acid

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

27. Decomposition Reactions
Another view of a decomposition reaction:

28. 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)

29. Decomposition is the reverse of synthesis
Ca(OH)2  CaO +H2O
HNO3  NO2 +H2O

30. Decomposition Exceptions
Carbonates and chlorates 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. Single Replacement Reactions
One element replaces a similar element in a compound.
A + BX  AX + B or
A + BX  BA + X

32. Single Replacement Reactions
Another view:

33. Single Replacement Examples
2Al(s) + 3Pb(NO3)2 (aq)  3Pb(s) + 2Al(NO3)3 (aq)
Al replaces Pb
Cl2(g) + 2 KBr(aq)  2KCl(aq) + Br2(g)
Cl replaces Br

34. 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.

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

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

37. : Activity Series
A list organized by the ease at which certain elements will undergo a chemical reaction.(p.266)
The order is determined by single-replacement reactions.

38. Activity Series Most Active Least Active
The most active element is placed at the top and can replace each of the elements below it.

39. 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.

40. 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 rx.

41. Double Replacement Reactions
The ions of two compounds exchange places in an aqueous solution to form two new compounds.
AX + BY  AY + BX

42. Double Replacement 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

43. …but there is more!!
Double displacement reactions only occur if at least one product is a solid liquid or a gas!
If both products are aqueous, then no reaction occurs!!
Check your solubility rules! Write in the state of your previous products

44. Some simple solubility rules
All Acids and alkali metal salts and NH4+ salts are soluble.
All nitrate and acetate salts are soluble.
All chlorides except AgCl and Hg2Cl2 PbCl2 are soluble.
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.

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

46. Mixed Practice
State the type, predict the products, and balance the following reactions:
BaCl2 + H2SO4  2HCl +BaSO4
Zn + CuSO4  Cu + ZnSO4
Cs + Br2  CsBr
CS2  C + S