1. Chapter 10
Chemical Reactions

2. Evidence of Chemical Reactions
Chemical Reaction: The process of one or more substances being rearranged to form a different substance
AKA – Chemical Change
Evidence:
Temperature change
Absorption of Heat (endothermic reaction)
Release of heat (exothermic reaction)
Color Change
Sometimes, reactions are so subtle they are hard to detect.

4. Representing Chemical Reactions
Reactants – Starting Substances (on the LEFT- HAND SIDE of the Equation)
Products – Ending Substances (on the RIGHT- HAND SIDE of the Equation)
Unlike in mathematics, where things are (=) equaled, in chemistry, reactions are directional ()
Reactant 1 + Reactant 2  Product 1 + Product 2

5. Representing Chemical Reactions
Reactant 1 + Reactant 2  Product 1 + Product 2 More correct Reactant 1 (state) + Reactant 2 (state)  Product 1 (state) + Product 2 (state) States are denotes as follows: (s) means solid (aq) means liquid (g) Means gas

6. Representing Chemical Equations in Words
Word Equations are used to indicate products and reactants of chemical reactions
Iron(s) + Chlorine(g)  Iron(III) Chloride (s)
In Word Equations:
Iron and Chlorine react to produce Iron (III) Chloride

7. Iron(s) + Chlorine(g)  Iron(III) Chloride (s)
Skeleton Equations
The skeleton equation gives more information than the word equation
It uses the chemical formulas (symbols) to describe a reaction
NOTE: THESE ARE NOT BALANCED EQUATIONS!!!
More information includes basic amounts of each element
Iron(s) + Chlorine(g)  Iron(III) Chloride (s)
Fe(s) + Cl2  FeCl3

8. Practice
Working independently on your white board, write skeleton equations for the following word problems:
hydrogen(g) +bromine(g)  hydrogen bromide (g)
Carbon monoxide (g) + oxygen (g)  carbon dioxide (g)
Potassium Chlorate (s)  Potassium Chloride(s) + Oxygen (g)

9. Practice Answers
Working independently on your white board, write skeleton equations for the following word problems:
hydrogen(g) +bromine(g)  hydrogen bromide (g)
H2(g) + Br2(g)  HBr (g)
2) Carbon monoxide (g) + oxygen (g)  carbon dioxide (g)
CO(g) + O2(g)  CO2 (g)
3) Potassium Chlorate (s)  Potassium Chloride(s) + Oxygen (g)
KClO3(g)  KCl(s) + O2(g)

10. Chemical Equations The Process: Write a skeleton equation
Remember the conservation of mass (matter is neither created nor destroyed, but can change shape and form)
Balance the equation so that the reactants and products are equal
When these three steps are complete, the product should be a balanced chemical reaction

11. How to Balance Chemical Reactions
Coefficient
The number written before either the products and/or reactants.
These are whole numbers
A “one” (1) is presumed
Coefficients start at “two” 2
H2 + Cl2  2HCl
The 2 in front of the HCl is the Coefficient

12. How to Balance Chemical Reactions
Write the skeleton equation for the reaction.
Count the atoms (number) of elements in the reactants
Count the atoms (number) of elements in the products
Change the coefficients to make the numbers of atoms of each element equal on both sides of the equation. Note: Never change the subscript
Write the coefficients in their lowest possible ratio
Check your work

13. How to Balance Equations – The T-Method
Equation: NaOH (aq) + CaBr2(aq)  Ca(OH)2(s) + NaBr(aq)
Reactants on this Side
Products on This Side
1- Na 1-OH 1-Ca 2-Br NaOH (aq) + CaBr2(aq) 2NaOH (aq) + CaBr2(aq) 2- Na 2-OH 1-Ca 2-Br They are Equal
1- Na 2-OH 1-Ca 1-Br Ca(OH)2(s) + 2NaBr(aq) 2- Na 2-OH 1-Ca 2-Br They are Equal
NOTE: Only Change 1 Coefficient, 1 Side at a Time.

14. Classifying Chemical Reactions
5 Main Types of Chemical Reactions
Synthesis Reaction
Combustion Reaction
Decomposition Reaction
Single-Replacement Reaction
Double-Replacement Reaction

15. Synthesis Reaction
A chemical reaction in which two or more products react to form a single product
A + B  AB
Synthesis can occur between elements and/or compounds
Element + Elements  Compound
Compound + Compound  Compound
Element + Compound  Compound

16. Synthesis Reaction Examples
2Mg + O2 ---> 2MgO
2H2 + O2 ---> 2H2O
2K + Cl2 ---> 2KCl
4Fe + 3O2 ---> 2Fe2O3
CaO + CO2 ---> CaCO3
Na2O + CO2 ---> Na2CO3
2KCl + 3O2 ---> 2KClO3
Ba(ClO3)2 ---> BaCl2 + 3O2

17. Predicting Products of Chemical Reactions
Class of Reaction
Reactants
Probable Products
Synthesis
Two or more substances
One compound

18. Combustion Reaction
Oxygen combines with substance and releases energy in the form of heat and light
Majority of combustion reactions are synthesis reactions
Not ALL combustion reactions are synthesis reactions

19. Combustion Reaction Examples
CxHy + O2 ---> CO2 + H2O
CH4 + O2 ---> CO2 + H2O
C2H6 + O2 ---> CO2 + H2O
C6H12O6 + O2 ---> CO2 + H2O
C2H5OH + O2 ---> CO2 + H2O
C21H24N2O4 + O2 ---> CO2 + H2O + NO2
C2H5SH + O2 ---> CO2 + H2O + SO2

20. Predicting Products of Chemical Reactions
Class of Reaction
Reactants
Probable Products
Synthesis
Two or more substances
One compound
Combustion
A metal and oxygen
A non-metal and oxygen
A compound and oxygen
The oxide of a metal
The oxide of a non-metal
Two or more oxides

21. Decomposition Reaction
A single compound breaks down into one or more elements and/or compounds
Opposite of the synthesis reaction
AB  A + B
Often require an energy source to occur.
Heat, light, electricity are some examples of energy

22. Decomposition Reaction Examples
HgO ---> Hg + O2
H2O ---> H2 + O2
MgCl2 ---> Mg + Cl2
FeS ---> Fe + S
CaCO3 ---> CaO + CO2
Na2CO3 ---> Na2O + CO2
KClO3 ---> KCl + O2
Ba(ClO3)2 ---> BaCl2 + O2

23. Predicting Products of Chemical Reactions
Class of Reaction
Reactants
Probable Products
Synthesis
Two or more substances
One compound
Combustion
A metal and oxygen
A non-metal and oxygen
A compound and oxygen
The oxide of a metal
The oxide of a non-metal
Two or more oxides
Decomposition
Two or more elements and/or compounds

24. Single Replacement Reaction
Also Called a Replacement Reaction
A reaction in which the atoms of one element replace the atoms of another element in a compound
A + BX  AX + B
One metal might replace another metal
Lithium and water is an example of a single replacement reaction

25. Single Replacement Reaction Examples
Cu + AgNO3 ---> Ag + Cu(NO3)2
Fe + Cu(NO3)2 ---> Fe(NO3)2 + Cu
Ca + H2O ---> Ca(OH)2 + H2
Zn + HCl ---> ZnCl2 + H2
ZnS + O2 ---> ZnO + S
K + H2O ---> KOH + H2
Fe + HCl ---> FeCl3 + H2
NaI + Br2 ---> NaBr + I2

26. Predicting Products of Chemical Reactions
Class of Reaction
Reactants
Probable Products
Synthesis
Two or more substances
One compound
Combustion
A metal and oxygen
A non-metal and oxygen
A compound and oxygen
The oxide of a metal
The oxide of a non-metal
Two or more oxides
Decomposition
Two or more elements and/or compounds
Single-replacement
A metal and a compound
A non-metal and a compound
A new compound and the replaced metal.
A new compound and the replaced non-metal

27. Double Replacement Reaction
The exchange of ions between TWO compounds
AY + BX  AX + BY
A and B would be cations
Y and X are anions
ALL products of a double-replacement reaction are either a precipitate, gas or water.
Precipitate: A solid produced during a chemical reaction

28. Guidelines for Double Replacement Reaction
Write the components of the reactants in a skeleton equation
Identify the cations and anions
Pair up each cation with the anion in the other compound
Write the formulas for the products using pairs from step 3.
Write the complete equation for the double-replacement reaction
Balance the equation

29. Double Replacement Reaction Examples
KOH + H2SO4 ---> K2SO4 + H2O
FeS + HCl ---> FeCl2 + H2S
NaCl + H2SO4 ---> Na2SO4 + HCl
AgNO3 + NaCl ---> AgCl + NaNO3
CaCO3 + HCl ---> CaCl2 + CO2 + H2O
K2SO3 + HNO3 ---> KNO3 + SO2 + H2O
NH4Cl + NaOH ---> NaCl + NH3 + H2O

30. Predicting Products of Chemical Reactions
Class of Reaction
Reactants
Probable Products
Synthesis
Two or more substances
One compound
Combustion
A metal and oxygen
A non-metal and oxygen
A compound and oxygen
The oxide of a metal
The oxide of a non-metal
Two or more oxides
Decomposition
Two or more elements and/or compounds
Single-replacement
A metal and a compound
A non-metal and a compound
A new compound and the replaced metal.
A new compound and the replaced non-metal
Double-Replacement
Two compounds
Two different compounds, one of which is often a sold, water or a gas

31. Reactions in Aqueous Solutions
Solutes: What is dissolved in a solution
Solvent: The liquid in which the solutes are dissolved
Aqueous Solution: A solution in which the solvent is water
HCl(g)  H+(aq) + Cl-(aq)
When HCl is dissolved in H2O, it dissociates into its separate parts of Hydrogen (Cation) and Chlorine (Anion)

32. Reactions that Form Precipitates
When the solutes mixed with the aqueous solvent have a solid product (precipitate)
2 AgNO3(aq) + MgBr2 → 2 AgBr(s) + Mg(NO3)2(aq) AB(aq) + CD(aq)  AD + CB
AB = Cation + Anion (in water)
CD = Cation + Anion (in water)
AD = Cation + Anion
CB = Cation + Anion
Use the Solubility Rules to determine if solid or aqueous

33. Solubility Rules for Ionic Compounds in Aqueous Solutions
All Salts of Group 1A are soluble
All Nitrates are Soluble
Chlorate, perchlorate and acetate are soluble
Majority of Chlorides, Bromides and Iodides are soluble. The exceptions are those made with Silver, Lead and Mercury.
The majority of Sulfates are soluble. The exceptions include barium, lead and strontium.
The majority of carbonates are insoluble. The exceptions are NH4+ and those of Group 1A.
The majority of hydroxides are insoluble. The exceptions are Barium, Strontium and the slightly insoluble Calcium and those of Group 1A.
The majority of Sulfides are insoluble. The exceptions are NH4+ and those of Group 1A and 2A.

34. Reactions that Form Precipitates
The majority of reactions within an aqueous solution are ionic
The ions completely dissociate into their separate identities
NaOH might become Na+ and OH-
Complete Ionic Equation: An ionic equation that shows al of the particles in a solution as they realistically exist within the solution
Spectator Ions: Ions that do not participate in a reaction and are usually not shown in ionic equations.

35. Three Types of Ionic Equations
Complete Ionic Equation: An ionic equation that shows all of the particles in a solution as they realistically exist within the solution
Spectator Ions: Ions that do not participate in a reaction and are usually not shown in ionic equations.
Net Ionic Equations: Ionic equations that only include the elements that participate in the reaction

36. Net Ionic Equation Example
2Na+ (aq) + 2OH-(aq) + Cu2+ (aq) + Cl- (aq)  2Na+ (aq) + 2Cl-(aq) + Cu(OH)2(s) NET IONIC EQUATION 2OH-(aq) + Cu2+ (aq)  Cu(OH)2(s)

37. Reactions that Form Water
Double-replacement reaction that occurs in an aqueous solution
Water is a product
Water molecules produced increase the amount of solvent within a solution
HBr (aq) + NaOH (aq)  H2O(l) + NaBr(aq)
H+ +Br- (aq) + Na+ + OH- (aq)  H2O(l) + Na+ + Br-(aq)
H+ + OH- (aq)  H2O(l)

38. Reactions that Form Gases
Double-replacement reaction that occurs in an aqueous solution
Gas is the product
Hydrogen gas of some form is often a product
2HI (aq) + Li2S(aq)  H2S(g) + 2LiI(aq)
2H+ + 2I- (aq) + 2Li+ + S2- (aq)  H2S(g) + 2Li+ + 2I-(aq)
2H+ + S2- (aq)  H2S(g)

39. Combining Reactions into a Single Chemical Equation
Overall Equation: The process of combining and representing two reactions into a single chemical equation
Process:
Reactants of the two reactions are written on the reactant side
Products of the two reactions are written on the products side
Any substances that are on both sides are crossed out and eliminated.
You know have a streamlined equation

40. Combining Reactions into a Single Chemical Equation
4FeS2 + 11O2  2Fe2O3 + 8SO2  8SO2 + 4O2  8SO3  8SO3 + 8H20  8H2SO4 
Reactants
Any Duplicates on BOTH Sides of the Eqation
Products
4FeS2 + 11O2
SO2
2Fe2O3 + 8SO2
8SO2 + 4O2
SO3
8SO3 
8SO3 + 8H20
8H2SO4 
4FeS2 + 15O2 + 8H20  2Fe2O3 + 8H2SO4