1. Chemical Reactions: An Introduction
Unit 6
Chemical Reactions:
An Introduction

2. Evidence of a Chemical Reaction
Color change
Temperature change
Formation of a gas (bubbles)
Formation of a precipitate
(a solid forming when 2 solutions are mixed together)

3. Principles of Chemical Reactions:
A chemical equation tells you what reactant chemicals are used and what product chemicals are formed.
A chemical equation does not tell you how long the chemical reaction will take, how to mix the chemicals, or at what temperature.

4. 2 H O2  2 H2O
The numbers in front of the chemicals, the coefficient, tell you the number of atoms and molecules involved, or the number of moles involved.
2 molecules of hydrogen are added to 1 molecule of oxygen makes (yields) 2 molecules of water.
2 moles of hydrogen are added to 1 mole of oxygen makes (yields) 2 moles of water.

5. Law of Conservation of Mass
You can not destroy or create substances in a chemical reaction. You simply change how they appear.
Mass at beginning = Mass at end of
of reaction reaction

6. } } To balance equations: a. Know what the reactants and products are
A + B  C + D
reactants products
Know the correct formula for each substance
c. Conserve atoms by placing coefficients in front of the chemicals so that you have the same number of atoms of each element on opposite sides of } }

7. Zn(s) + 2 HCl(aq)  ZnCl2 (aq) + H2 (g)
Notation of phase may be used.
s = solid
L = liquid
g = gas
aq = aqueous (dissolved in water)
Zn(s) HCl(aq)  ZnCl2 (aq) + H2 (g)

8. Balancing equations using molecule model kits:
H O  H2O

9. Element colors
Hydrogen – Yellow
Carbon – Black
Nitrogen – Blue
Oxygen – Red
Chlorine - Green

10. Types of Chemical Reactions
Synthesis X + Y  XY
Decomposition XY  X + Y
Combustion CxHyYz + O2  CO2 + H2O
Single Replacement A + XY  AY + X
Double Replacement AB + XY  AY + XB

11. Types of chemical reactions:
Synthesis (or combination): combining 2 or more small molecules or atoms into one larger molecule Synthesis X + Y  XY
H2 (g) O2 (g)  H2O (g)

12. Decomposition: breaking a large molecule into 2 or more smaller molecules or atoms
Decomposition XY  X + Y
(NH4)2Cr2O7(s)  N2 (g) + H2O (g) + Cr2O3 (s)
Combustion: a hydrocarbon molecule combining with oxygen to make CO2 and H2O
Combustion CxHyYz + O2  CO2 + H2O
C2H6O (g) + O2 (g)  CO2 (g) + H2O (g)

13. Single replacement: an element exchanges places with another element in a compound to make a new element and a new compound
Single Replacement A + XY  AY + X
AgNO3 (aq) + Cu (s)  Cu(NO3)2 (aq) + Ag (s)
Double replacement: when 2 compounds exchange partners to make 2 new compounds
Double Replacement AB + XY  AY + XB
FeCl3 (aq) + NaOH (aq)  Fe(OH)3 (s) + NaCl (aq)

14. Writing balanced ionic equations for chemicals dissolving in H2O
NaCl (s)  NH4Cl (s)  CaCl2 (s)  (NH4)2CO3 (s) 

15. AgNO3 (s)  CuCl2 (s)  NaHCO3 (s)  Na2SO4 (s) 

16. Types of Chemical Reactions
Synthesis X + Y  XY
Decomposition XY  X + Y
Combustion CxHyYz + O2  CO2 + H2O
Single Replacement A + XY  AY + X
Double Replacement AB + XY  AY + XB

17. .50 mol mol
Fe2O C  Fe CO 2
____g g ____g ____g

18. CaO (s) + H2O (L)  Ca(OH)2 (s)
Some reactions give off energy. These are called exothermic chemical reactions.
CaO (s) H2O (L)  Ca(OH)2 (s)
Some reactions absorb energy. These are called endothermic chemical reactions.
Ba(OH)2.8H2O(s) + NH4NO3 (s)  Ba(NO3)2(aq) + NH3(g) +H2O(L)
Some chemical reactions are reversible.
2 H2 (g) + O2 (g)  2 H2O (g) + energy
energy H2O (L)  2 H2 (g) + O2 (g)

19. Review 2H2O2  2H2O + O2 3C + 2Fe2O3  3CO2 + 4 Fe
1. 2C3H8O + 9O2  6CO H2O
2H2O2  2H2O + O2
3C + 2Fe2O3  3CO Fe
6CO H2O  C6H12O O2
2NaCl + Pb(NO3)2  PbCl NaNO3
2 H2 + O2  2 H2O
2. Synthesis – f, decoposition – b, single replacement – c, double replacement – e, combustion – a
(d doesn’t fit any of these)
3. 4Fe O2  2 Fe2O3
4. Ba(NO3)2  Ba NO3-1
AlCl3  Al Cl-1
(NH4)3PO4  3NH PO4-3
mol mol
CaCO HCl  CaCl2 + H2CO3
20.02g g g g

20. Blank Periodic Table (you wrote on)
Use on the exam:
Periodic Table
Formula sheet
Mole Wheel
Common Ions
Calculator
Blank Periodic Table (you wrote on)