CHEM 121
Chapter 5
1
The Mole
•
•
•
•
12 eggs =
12 bagels =
6.02 x 1023 hydrogen atoms =
6.02 x 1023 water molecules =
How many water molecules are in 3.5 moles of water?
2
Moles of Elements in a Formula
How many moles of each element are in 1 mole of water?
How many moles of each element are in 1 mole of glucose?
3
Molar Mass
•
•
Examples:
Carbon
Water
Atomic mass?
Molecular mass?
Molar mass?
Molar mass?
4
Calculations with Molar Mass
You measure out 10.0 g of water.
How many moles of water do you have?
If a piece of metal displaces 2.2 mL water,
how many water molecules has it displaced?
(Assume the density of water is 1.0 g/mL.)
5
Chemical Equations
Physical Change:
Chemical Change:
Chemical Equation:
6
Types of Reactions
Mg
A
+
B
+
O
O
7
Types of Reactions
A
H
B
O
H
8
Types of Reactions
•
A
+
B
C
•
A
B
+
C
D
9
Chemical Equations
_____________ and ___________ involved in change
1.
2.
3.
4.
5.
Ex. Reaction of magnesium solid and oxygen
10
Reaction Equivalents
C3H8 (g) + 5 O2 (g)  3 CO2 (g) + 4 H2O (g)
1
1
1
5
2
molecule C3H8 reacts with _______ molecules O2
molecule C3H8 produces _______ molecules CO2
molecule C3H8 produces _______ molcules H2O
molecules O2 produces _______ molecules CO2
molecules C3H8 produces _______ molecules CO2
11
Ionic Equations
• Molecular equations
–
• Total ionic equations
–
• Net ionic equations
–
Example: HCl and NaOH
Precipitation Reactions
• Type of replacement reaction
•
Example: Aqueous sodium iodide and lead (II) nitrate
13
Stoichiometry
the study of mass relationships in chemical equations
Can’t compare mass to mass
Go to moles first
14
Reaction Calculations
1.
2.
3.
4.
15
Sample Problem
How much carbon dioxide (in grams) is produced
when 3.00 g of ethanol (C2H6O) combusts in air?
How much oxygen gas is used up to combust 5.00 g
of ethanol?
16
5-minute review
How many grams of oxygen are needed to react
with 1 mole of CH4 to create water?
Hint: carbon dioxide is also a product.
17
Yields
• Theoretical yield:
• Actual yield:
–
• Percent yield:
18
Limiting Reactants
What if we have:
8 scoops of ice cream
6 cherries
100 mL of syrup.
How many sundaes can we make?
19
Chemical Reactions Involving
a Limiting Reactant
hydrazine (N2H4) and dinitrogen tetraoxide are
liquids that ignite to form nitrogen gas and water
vapor
How many grams of nitrogen gas form when 100. g of
N2H4 and 200. g of dinitrogen tetraoxide are mixed?
20
Redox Reactions
• Reduction and oxidation
• Movement of e- from one reactant to another
• 2 Mg (s) + O2 (g) --> 2 MgO (s)
• LEO GER
• Reducing agent? Oxidizing agent?
21
Oxidation Numbers (O.N.)
•
•
•
•
•
•
Any element has O.N. =
1A(1) ions =
2A(2) ions =
H ion can only =
Oxygen ion only =
Halogen ions usually =
The sum of all atoms O.N. in a compound =
Examples: ZnCl2
sulfur trioxide
potassium sulfate
22
3-minute review
What is the O.N. of each atom in CaCO3?
23
Redox Reaction?
CaO (s) + CO2 (g) → CaCO3 (s)
24
3-minute Review
What’s been oxidized in each reaction?
Cu (s) +
AgNO3 (aq) →
N2 (g) + H2 (g)
→
Ag (s) + Cu(NO3)2 (aq)
NH3 (g)
25