1. Science 1206
Unit 2: Chemistry

2. Chemical Reactions
Unit 2: Chemistry

3. Chemical Reactions
Chemical reactions are a part of our everyday life. Brushing our teeth, getting a ride to school in the family car, digesting food, and many others are all examples of chemical reactions. The reactions may be very complex, as in the creation of explosives, or they may be very simple, as in the reaction of a bathroom cleaner and a stain. The basic structure of a chemical reaction is the creation of some new substance(product) from the reaction of one, two, or more, initial substances(reactants).

4. Reactants —> Products 2 Na + CaO —> Na2O + Ca Sodium reacts with calcium oxide to produce sodium oxide and calcium

5. Types of Reactions
There are five basic types of chemical reactions. These include.
1. Synthesis / Simple Composition Reactions
2. Decomposition / Simple Decomposition Reactions
3. Double Replacement/Double Displacement
4. Single Replacement/Single Displacement
5. Combustion Reactions
6. Other

6. The Law of Conservation of Mass
In a chemical reaction, the total mass of the reactants is always equal to the total mass of products.
Mass(reactants) = Mass(products)
Example 1:
NaCl + CaO —> Na2O + CaCl2
 12g 20g —> 15g 17g
Mass(reactants) = 12g g = 32g
Mass(products) = 15g g = 32g

7. Example 2:
NaCl + CaO —> Na2O + CaCl2
18g 40g —> 30g ?g
Mass(reactants) = 18g + 40g = 58g
Mass(products) = 20g + ?g = 58g

8. Types of Chemical Equations:
There are three basic representations of reaction equations. These are; Word Equations a way of writing chemical reactions in which the left side of the equation lists the names of all the reactants and the right side of the equation lists the names of all of the products. Let’s look at the chemical reaction where iron reacts with oxygen to produce iron(III) oxide(rust) Example: Iron + Oxygen —> Iron (III) oxide

9. Skeleton Equation a representation of a chemical reaction in which formulas of the reactants are connected to the formulas of the products by an arrow.
Example: Fe + O2 —> Fe2O3

10. Balanced Equation an equation in which the reactants and products contain equal number of each type of atoms. Example: 4 Fe + 3 O2 —> 2 Fe2O3 Four formula units of iron react with three molecules of oxygen to produce two formula units of iron(III) oxide. Example: CH4 + 2O2 —> CO2 + 2 H2O One molecule of methane reacts with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water.

11. In a chemical reaction it is very important that the numbers of individual atoms on one side of the equation is equal to the number of individual atoms on the other side of the reaction. In the above reaction equation, for example, you will notice that there are four iron atoms on both the reactant and product sides of the equation.

12. Type 1: Synthesis / Simple Composition Reactions
to synthesize is to ‘create’
when elements or compounds combine to form a new substance a synthesis reaction occurs
can be compared to the formation of a new ‘couple’ from two individuals
Model:
A + B —> AB
element element —> compound
simple compound + simple compound —> complex compound

13. Example1:Hydrogen and oxygen react to produce water
word equation: hydrogen + oxygen —> water
skeleton equation: H2 + O2 —> H2O
balanced equation: 2 H2 + O2 —> 2 H2O

14. Example 2:Hydrochloric acid and ammonia react to produce ammonium chloride
word equation: Hydrochloric acid + ammonia —> ammonium chloride
skeleton equation: HCl + NH3 —> NH4Cl
balanced equation: HCl + NH3 —> NH4Cl same as skeleton equation

15. Example 3: Write word, skeleton and balanced chemical equations for the synthesis of aluminum chloride
word equation:
skeleton equation:
balanced equation:

16. Type 2:Decomposition / Simple Decomposition Reactions
to decompose is to ‘break down’
when compounds break down into two or more elements or compounds a decomposition reaction occurs.
can be compared to the ‘break-up’ of a couple

17. Model:
AB —> A + B
compound —> element element
complex compound —> simple compound + simple compound

18. Example 1: Nitrogen triodide decomposes to its individual elements
word equation: Nitrogen triodide —> nitrogen + iodine
skeleton equation: NI3 —> N2 + I2
balanced equation 2 NI3 —> N I2

19. Example 2: Sodium chloride decomposes to its individual elements
word equation: Sodium chloride —> sodium chlorine
skeleton equation: NaCl —> Na + Cl2
balanced equation: 2 NaCl —> 2 Na + Cl2

20. Example 3: Write a word, skeleton and balanced chemical equation for the decomposition of gallium sulfide.
word equation:
skeleton equation:
balanced equation:

21. Type 3: Single Replacement/Single Displacement
when an element replaces another element in a compound to form a new substance a single replacement reaction occurs
think of this kind of reaction as a person ‘cutting in’ on a couple dancing
Model:
AC + B —> A + BC
compound + element —> compound + element

22. Example1: Sodium reacts with calcium oxide to produce .......
word equation: sodium + calcium oxide —> sodium oxide + calcium
skeleton equation: Na + CaO —> Na2O + Ca
balanced equation: 2Na + CaO —> Na2O + Ca

23. Example 2:Calcium iodide reacts with chlorine to produce calcium chloride and iodine
word equation: calcium iodide + chlorine —> calcium chloride + iodine
balanced equation: CaI2 + Cl2 —> I2 + CaCl2

24. Example 3: Demo
Copper reacts with silver nitrate to produce
word equation: Copper + silver nitrate —>
balanced equation: Cu + AgNO3 —>

25. Example 4: Demo
 Magnesium reacts with silver nitrate to produce
word equation: magnesium + silver nitrate —>
balanced equation: Mg + AgNO3 —>

26. Type 4:Double Replacement/Double Displacement
when an element in one compound replaces an element in a another compound to form two new substances a double replacement reaction occurs
think of this type of reaction as two couples dancing and part ways through the dance they switch partners

27. Model:
AC + BD —> AD + BC
compound + compound —> compound + compound

28. Example 1: Sodium chloride reacts with calcium oxide to produce .........
word equation: sodium chloride + calcium oxide —> sodium oxide + calcium chloride
skeleton equation: NaCl + CaO —> Na2O + CaCl2
balanced equation: 2 NaCl + CaO —> Na2O CaCl2

29. Example 2: Magnesium sulfide reacts with aluminum oxide to produce .....
word equation: magnesium sulfide + aluminum oxide —>
balanced equation: MgS Al2O3 —>

30. Example 3: Gallium sulfate reacts with iron III nitrate to produce ...
word equation: Gallium sulfate + iron III nitrate —>
balanced equation: Ga2(SO4) Fe(NO3)3 —>

31. Example 4: Demo
Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide and hydrogen gas
word equation: Calcium carbonate + hydrochloric acid —> calcium chloride carbon dioxide + hydrogen
balanced equation CaCO3 + HCl(aq) —> CaCl CO2 + H2

32. Neutralization A neutralization reaction is a special case of a double replacement reaction that involves the reaction of an acid substance with a base substance to produce a salt and water. Model: Acid + base —> salt + water

33. Example 5: Hydrochloric acid reacts with sodium hydroxide to produce ...
word equation: hydrochloric acid + sodium hydroxide —>
balanced equation: HCl + NaOH —>

34. Type 5:Hydrocarbon Combustion Reactions
rapid reaction of a substance with oxygen to produce an oxide
fuel + oxygen —> oxides + energy
One of the most important current fuel sources on this planet is hydrocarbons (Carbon and Hydrogen)
Model:
hydrocarbon + oxygen —> carbon dioxide + water vapour

35. Example 1: Write a word and reaction equation for the complete combustion of butane.
word equation: butane + oxygen —> carbon dioxide + water vapour
skeleton equation: C4H O2 —> CO2 + H2O
reaction equation: 2 C4H O2 —> 8 CO H2O

36. Example 2: Write a word and reaction equation for the complete combustion of methane.
word equation: methane + oxygen —> carbon dioxide + water vapour
reaction equation: CH O2 —> CO H2O

37. Example 3: Write a word and reaction equation for the complete combustion of gasoline(C8H18) . word equation: gasoline + oxygen —> carbon dioxide + water vapour reaction equation: C8H O2 —> 8CO2 + 9H2O 2 C8H O2 —> 16 CO H2O

38. Example 4: Write a word and reaction equation for the complete combustion of propane(C3H8). word equation: gasoline + oxygen —> carbon dioxide + water vapour reaction equation: C3H8 + 5 O2 —> 3 CO2 + 4 H2O

39. Example 5: Write a word and reaction equation for the complete combustion of cyclopropane(C3H6).
word equation: cyclopropane + oxygen —> carbon dioxide + water vapour 
reaction equation:
2 C3H O2 —> 6 CO H2O

40. Incomplete Combustion
When materials burn and the conditions are not perfect the combustion is incomplete. The materials do not completely change and four products are produced instead of two.

41. Model:
hydrocarbon + oxygen —> carbon monoxide + carbon + carbon dioxide + water vapour
2 C4H O2 —> 8 CO C CO H2O
Other
All reactions that do not fit into the categories above.

42. Evidence of Chemical Reactions
Precipitate forms: New substance forms which has a lower solubility than the original substance 
Gas forms: A new substance is formed which is a gas in the lab conditions of temperature and pressure
Colour change: A new substance is formed which has a different colour than the original substance
Energy Change: Heat produced or used. Energy is released or absorbed to obey the Law of Conservation of Energy
Releases energy - Exothermic
Absorbs Energy - Endothermic

43. Phase of compounds and elements at room Temperature
Denoted in subscripts at the end of an element or compound name
(s) solid
(l) liquid
(g) gas
(aq) aqueous - soluble in water

44. Determining Phase - in chemical equations
Elements - use periodic table
Molecular compounds - personal experience - see table below

45. Ionic Compounds
all ionic compounds not in water are solids
when ionic compounds are placed in water some completely dissociate, or completely dissolve (are soluble), while other ionic compounds do not
Solubility of Ionic Compounds
the solubility table on your periodic table is required to determine the phase of ionic compounds in water. When one of the reactants has an (aq) there is water present and therefore you need to determine the phase of the products.

46. to use the table find the anion (the negative part of the compound)
example BaSO4 - look up the SO4 in the table. Most are highly soluble but not Ba2+. So we would write BaSO4 (s)
example CuSO4 - look up the SO4 in the table. Most are highly soluble and Cu2+ is not in the list of those that have low solubility. So we would write CuSO4(aq)