Transcript Ch. 16: Solutions - Quynh Nguyen Official Website

Ch. 5: Chemical
Quantities and
Reactions
Chem 20
El Camino College
1
Properties and Changes

Physical changes are changes of the
physical form that don’t alter the chemical
identity of a substance (e.g., boiling,
melting, crushing, tearing)
2
Chemical Changes

In chemical changes, one substance is destroyed
and a new one forms (often with change in color,
emission of heat, light, or sound, or change in
taste or odor).

Is chopping wood a physical or chemical change?
Is burning wood a physical or chemical change?

3
4
5
6
7
Example:
Identify whether each is a physical or
chemical change
Beating eggs
physical change
chemical change
Cooking eggs
physical change
Ripping paper
Boiling water
physical change
Lighting a match chemical change
Dissolving Kool-Aid drink mix physical change
Freezing Kool-Aid physical change
8
State Symbols
(s) solid
 (l) liquid Hg(l), Br2(l), H2O(l)

(g) gas
 (aq) aqueous or dissolved in water

9
Balancing Reactions
Use coefficients (big #s) to balance rxns
 Don’t change cmpd formulas (small #s within a
cmpd)
 If possible, balance an element by itself last
 Don’t end with fractions, use lowest whole #s
 Balance polyatomic ions as a whole package.

10
Ex.
2 H2(g)
+
4H
2O
O2(g)  2 H2O(l)
4H
2O
11
12
13
Examples
CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g)
1C
1C
4H
4H
4O
4O
4 Fe(s) + 3 O2(g)  2 Fe2O3(s)
4 Fe
4 Fe
6O
6O
14
15
2 HClO(aq)  H2O(l)
+
Cl2O(g)
Cu(s) + 2 AgNO3(aq)Ag(s)+Cu(NO
2
3)2(aq)
Mg(s)+ H2SO4(aq)  H2(g)+ MgSO4(aq)
16
Reaction Types:
Combination Reactions
 Decomposition Reactions
 Single Replacement Reactions
 Double Replacement Reactions

17
What type is it? Look at what
is reacting.
Element + element: Combination
 One compound: Decomposition
 Element + Compound: Single Replacement
 Compound + Compound: Double Replacement

18
Write the rxn type

2 Mg(s) + O2(g)  2 MgO(s) combination
single
replacement

Mg(s) + CuCl2(aq)  MgCl2(aq) + Cu(s)

2 HgO(s)  2 Hg(l) + O2(g)

NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq) double
replacement

CuCO3(s)  CuO(s) + CO2 (g)

Li2SO4(aq)+BaCl2(aq)BaSO4(s)+2LiCl(aq)
decomposition
decomposition
double
replacement
Combination Reactions
A + X  AX
Ex. Magnesium is burned in air to form
magnesium oxide.
2Mg(s) + O2(g)  2MgO(s)
20
21
22
Combination Reactions
Examples
Ex. Sodium is combined with oxygen to
form sodium oxide.
4 Na(s) + O2(g)  2 Na2O(s)
Ex. Aluminum and bromine react to form
aluminum bromide.
2Al(s) + 3Br2(l) 
2 AlBr3(s)
23
Combination Reactions
24
Decomposition Reactions
AX  A + X
Ex. Sodium hydride decomposes to form
sodium and hydrogen.
2 NaH(s) 
2 Na(s)+ H2(g)
25
Decomposition Reactions
Ex. Copper(II) carbonate is heated to give
copper(II) oxide plus carbon dioxide.
CuCO3(s)

CuO(s) + CO2(g)
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Decomposition Reaction
27
Balance, write the rxn type
4 K(s) + O2(g) 
2 K2O(s)
combination
2 KClO3(s) KCl(s) + 3O2(g) decomposition
4 P(s) + 3 O2(g) 
2 P2O3(s) combination
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K2CO3(s)  K2O(s) + CO2(g) decomposition
2 H2O2(l)  2 H2O(l) + O2(g)
2 FeCl3(s) 
2 Fe (s) + 3 Cl2(g)
decomposition
decomposition
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Single Replacement Rxns
A + BX  AX + B
Ex. Copper is added to silver nitrate solution to form
aqueous copper(II) nitrate and silver.
Cu(s) + 2 AgNO3(aq) Cu(NO3)2(aq) +2 Ag(s)
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31
Fig. 8-6a, p. 213
32
Fig. 8-6b, p. 213
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Single Replacement Rxns
Ex. Sodium reacts with hydrochloric acid to
form sodium chloride solution and hydrogen.
2 Na(s) + 2 HCl(aq) 
2 NaCl(aq) + H2(g)
Ex. Sodium reacts with water to form sodium
hydroxide solution and hydrogen.
2 Na(s) + 2 H2O(l)  2 NaOH(aq) + H2(g)
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35
Fig. 8-1a, p. 200
36
Fig. 8-1b, p. 200
Balance, write the rxn type
BaCl2 (s) Ba(s) + Cl2 (g)
3 K(s) +
decomposition
AlCl3(aq)  3 KCl(aq) +
Al(s)
single replacement
37
Balance, write the rxn type
Cu2CO3(s) Cu2O(s) + CO2(g)
decomposition
2 Li(s) + 2 H2O(l)  2 LiOH(aq) + H2(g)
single replacement
38
Double Replacement Rxns
AX + BY

AY + BX
Ex. Lead(II) nitrate soln and hydrochloric acid form
solid lead(II) chloride and nitric acid (HNO3(aq)).
Pb(NO3)2(aq)+ 2 HCl(aq) 
PbCl2(s)+2 HNO3(aq)
Ex. Liquid (H2O) forms in acid-base neutralization
reactions: Solns of hydrobromic acid and lithium
hydroxide react to form lithium bromide soln and
water.
HBr(aq) + LiOH(aq)  LiBr(aq) + H2O(39l)
40
41
Double Replacement
Reaction
42
Balance, write the rxn type
H2(g) + Br2(l)  2 HBr(g)
combination
CuO(s) +
2 HI(aq)  CuI2(aq) +
H2O(l)
double replacement
43
Balance, write the rxn type
Zn(s) + Br2(l)
2 K(s) + 2 H2O(l)
 ZnBr2(s)
combination
 2 KOH(aq) + H2(g)
single replacement
2 AlH3(s)  2 Al (s) + 3 H2(g)
decomposition
44
Oxidation and Reduction

Oxidation
Oxidation # gets more positive
 Hydrogens may be removed
 Oxygens may be added


Reduction
Oxidation # gets more negative
 Hydrogens may be added
 Oxygens may be removed

45
Oxidation #

For all the examples we’ll do in class the
oxidation # is the same as the charge
oxidation number
 Cu2+
2+
1F
0
 O2
3+
 Fe3+
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Oxidation #

You may have to determine the charge of
an ion in a cmpd
CuBr
 Fe2S3
 Ag3P
 Br2

ox # Cu = 1+, ox # Br = 1ox # Fe = 3+, ox # S = 2ox # Ag = 1+, ox # P = 3ox # Br = 0
47
Oxidation #

Write the oxidation # above each element
in the rxn, both in reactants and products
0
1+ 10
3+1 3 Na(s) + AlF3(aq)  3 NaF(aq) + Al(s)
changes in ox #
ox # Na 0 1+
ox # Al
3 + 0
ox # F
1- 148
Oxidation #
When ox # gets more positive, write “Element
is oxidized, it’s the reducing agent”
 When ox # gets more negative, write
“Element is reduced, it’s the oxidizing agent”

changes in ox #
ox # Na 0 1+
ox # Al
3 0
ox # F
1- 1-
Element is oxidized, it’s the reducing agent
Element is reduced, it’s the oxidizing agent
49
Oxidation #
Write the ox # above each element in the rxn
0
2+ 10
2+ 1 Zn(s) + CuCl2(aq)  ZnCl2(aq) + Cu(s)

changes in ox #
show oxidized and reduced elements
show reducing and oxidizing agents
ox # Zn 0 2+
ox # Cu 2+ 0
ox # Cl 1- 1-
Element is oxidized, it’s the reducing agent
Element is reduced, it’s the oxidizing agent
50
Oxidation #
Write the ox # above each element in the rxn
0
1+ 10
1+ 1 F2(g) + 2 KCl(aq)  2 KF(aq) + Cl2(g)

changes in ox #
ox # F 0 1ox # K 1+ 1+
ox # Cl 1- 0
show oxidized and reduced elements
show reducing and oxidizing agents
Element is reduced, it’s the oxidizing agent
Element is oxidized, it’s the reducing agent
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The Mole (mol)




1 mol of things is 6.02 x 1023 things
6.02 x 1023 is Avogadro’s #
1 mol N2 molecules=6.02 x 1023 molecules
As a conversion factor
1 mol N2
6.02 x 1023 N2 molecules
mol  molecules
How many N2 molecules in 9.5 x 10-10 mol?
(
)
9.5 x 10-10 mol N2 6.02 x 1023 N2 molecules = 5.7 x 1014 molecules
1 mol N2
52
53
mol  molecules or atoms
many molecules in 5.55 x 10-2 mol of
ammonia?
How
5.55 x 10-2 mol NH3
How
(
6.02 x 1023 molecules
1 mol NH3
) = 3.34 x 10
22
molecules
many atoms in 599 mol Fe?
599 mol Fe
(
6.02 x 1023 atoms
1 mol Fe
x 10
) = 3.61atoms
54
26
molecules or atoms  mol
many moles in 2.25 x 1016 molecules of
oxygen?
How
2.25 x 1016 molecules
How
(
1 mol O2
6.02 x 1023 molecules
)
= 3.74 x 10-8 mol
many moles in 399 water molecules?
399 molecules H2O
(
1 mol H2O
6.02 x 1023 molecules
) = 6.63 x 10
55
-22
mol
Molar Mass
Molar mass is the mass of a substance in g/mol
 Use the periodic table, go to the hundredths
place
 The units are
grams
mol

• Example: Find the molar mass of water
• H2O
H
2(1.01 g/mol)= 2.02 g/mol
O
= 16.00 g/mol
= 18.02 g/mol
56
Molar Mass
Find the molar mass of CaCl2
 CaCl2
Ca
= 40.08 g/mol
Cl 2(35.45 g/mol) = 70.90 g/mol
= 110.98 g/mol
Find the molar mass of AlBr3
 AlBr3
Al
= 26.98 g/mol
Br 3(79.90 g/mol) =239.70 g/mol
= 266.68 g/mol
57
Solved Example: mol  g

How many g in 16.5 mol N2?
N2 2(14.01 g/mol) = 28.02 g/mol
16.5 mol 28.02 g N2 = 462 g N
2
1 mol
58
mol  g

How many g in 10.4 mol Li?
Li 6.94 g/mol
10.4 mol 6.94 g Li
1 mol
= 72.2 g Li
59
mol  g

How many g in 3.33 mol CO2?
C
12.01 g/mol
O 2(16.00 g/mol) = 32.00 g/mol
= 44.01 g/mol
3.33 mol 44.01 g CO2 = 147 g CO
2
1 mol
60
Solved Example: g  mol

How many mol in 9.80 g O2?
O2 2(16.00 g/mol) = 32.00 g/mol
9.80 g
1 mol
32.00 g
= .306 mol O2
61
g  mol

How many mol in 55.55 g Al?
Al 26.98 g/mol
55.55 g
1 mol
26.98 g Al
= 2.059 mol Al
62
How many g in 121 mol H2?
H2
2.02 g/mol
121 mol
2.02 g H2
1 mol
= 244 g H2
How many moles in 8798 molecules of O2?
8798 molecules
(
1 mol O2
6.02 x 1023 molecules
)
= 1.46 x 10-20 mol
63
Conversions



g
mol
atoms, molecules
atoms, molecules
use molar mass
mol use 6.02x1023
mol
grams
You cannot convert directly from
atoms or molecules to grams
64
How many moles in 53.3 g H2O?
53.3 g 1 mol H2O = 2.96 mol H O
2
18.02 g
How many molecules in 9.9 x 10-22 mol of Cl2?
9.9x10-22 mol Cl2 6.02 x 1023 molecules
1 mol Cl2
= 6.0 x 102 molecules
65
g  molecules or atoms
(g  mol  molecules or atoms)

How many hydrogen molecules in 1.00 g?
H2
1.00g H2 1 mol H2
2.02 g

2(1.01 g/mol) = 2.02 g/mol
6.02x1023 molecules = 2.98x1023 molecules
1 mol H2
How many sodium atoms in 39.8 g?
Na
39.8g Na 1 mol Na
22.99 g
22.99 g/mol
6.02x1023 atoms
1 mol Na
= 1.04x1024 atoms
66
molecules or atoms  g
(molecules or atoms  mol  g)
How many g in 259,000 Mg atoms?
Mg
259,000 Mg atoms
1 mol Mg
6.02x1023
atoms
24.31 g/mol
24.31 g
1 mol Mg
=
1.05 x 10-17 g Mg
How many g in 3.98x1020 molecules F2?
F2
2(19.00 g/mol) = 38.00 g/mol
3.98x1020 molecules 1 mol F2
6.02x1023
molecules
38.00 g
1 mol F2
=
2.51x10-2 g F2
67

How many molecules in 3.33 mol glucose
(C6H12O6)?
3.33 mol
6.02x1023 molecules = 2.00x1024
mol C6H12O6
molecules
68
Conversion Factors from
Chemical Equations
3 H2(g) + N2(g)

2 NH3(g)
Conversion factors from the balanced eqn
1 molecule N2 3 molecules H2
3 molecules H2 1 molecule N2
2 mol NH3 3 mol H2
3 mol H2 1 mol N2
69
moles A  moles B
3 H2(g) + N2(g)

2 NH3(g)
Example: If 6.54 mol N2 react, how many mol NH3 form?
6.54 mol N2 2 mol NH3
1 mol N2
=
13.1 mol NH3
If 10.3 mol H2 react, how many mol N2 react?
10.3 mol H2 1 mol N2
3 mol H2
=
3.43 mol N2
70
g A  moles B
3 H2(g) + N2(g)

2 NH3(g)
If 3.50 g H2 react, how many mol N2 react?
3.50 g H2 1 mol H2
2.02 g H2
1 mol N2
3 mol H2
= 0.578 mol N2
If 19.0 g N2 react, how many mol H2 react?
19.0 g N2 1 mol N2
28.02 g
3 mol H2
1 mol N2
= 2.03 mol H2
71
3 H2(g) + N2(g)

2 NH3(g)
If 110.4 g NH3 form, how many g H2 reacted?
110.4 g NH3 1 mol NH3
3 mol H2
2.02 g = 19.6 g H
2
17.04 g NH3 2 mol NH3 1 mol H2
If 5.33 x 1025 molecules H2 react, how many g N2 react?
5.33 x 1025
H2 molecules
1 mol H2
1 mol N2 28.02 g N2
6.02 x 1023 3 mol H2 1 mol N2
molecules
= 827 g N2
72