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Title: Flashcards for Unit 12


1
Flashcards for Unit 12
2
Equilibrium
  • Rate of forward process
  • Rate of reverse process

3
Conditions for Equilibrium
  • 2-way process
  • Closed System

4
Dynamic Equilibrium
  • Macroscopic level looks constant.
  • Microscopic level lots of action

5
Types of Equilibria
  1. Physical Phase Solution
  2. Chemical

6
A solution at equilibrium must be
  • Saturated

7
Phase Equilibrium
  • H2O(l) ? H2O(g)

8
Solution EquilibriumIonic Cmpd
  • NaCl(s) ? Na(aq) Cl-(aq)

9
Solution EquilibriumCovalent Cmpd
  • C6H12O6(s) ? C6H12O6(aq)

10
H2O(g) ? H2O(l)
  • Phase Equilibrium

11
NH4Cl(s) ? NH4(aq) Cl-(aq)
  • Solution Equilibrium

12
Chemical Equilibrium Haber Synthesis
  • N2(g) 3H2(g) ? 2NH3(g) heat

13
LeChateliers Principle
  • A system at equilibrium will respond to remove a
    stress

14
Whats a stress for a chemical system?
  • Change in temperature, pressure, or concentration

15
Catalyst
  • Substance that increases the rate of a chemical
    reaction without itself being consumed.

16
Catalyst
  • Does not shift the equilbrium point the
    equilibrium concentrations are the same. You
    just get to equilibrium quicker.

17
At what temperature can H2O(s) and H2O(l) exist
in equilibrium?
  • 0?C or 273K

18
At what temperature can H2O(g) and H2O(l) exist
in equilibrium?
  • 100?C or 373K

19
Pressure Changes
  • Only affect systems that have a gas in them

20
An increase in pressure favors which side?
  • CO2(g) ? CO2(aq)

When P ?, more CO2 dissolves!
21
N2(g) 3H2(g) ? 2NH3(g) heat
  • Equilibrium shifts to right.
  • Concentration of H2 ?. Concentration of NH3 ?.
    Temperature ?

What happens?
Stress
22
N2(g) 3H2(g) ? 2NH3(g) heat
  • Shifts to the side with fewer moles of gas, in
    this case the right.

4 moles
2 moles
How does this system respond to an increase in
pressure?
23
N2(g) 3H2(g) ? 2NH3(g) heat
  • Shifts to the side with more moles of gas, in
    this case the left.

How does this system respond to a decrease in
pressure?
24
H2(g) I2(g) heat ? 2HI(g)
  • This system has the same of moles on each side.
    It cannot respond to pressure changes.

2 moles
2 moles
How does this system respond to a decrease in
pressure?
25
NaCl(s) ? Na(aq) Cl-(aq)
  • This system has no gases. It does NOT respond to
    pressure changes.

How does this system respond to a change in
pressure?
26
N2(g) 3H2(g) ? 2NH3(g) heat
  • Equilibrium shifts to the left.
  • Concentration of N2 H2 ?. Temperature ?.

Stress
What happens?
27
N2(g) 3H2(g) ? 2NH3(g) heat
  • Equilibrium shifts to the right.
  • Concentration of N2 H2 ?. Temperature ?.

Stress
What happens?
28
N2(g) 3H2(g) ? 2NH3(g) heat
  • Equilibrium shifts to the left.
  • Concentration of N2 ?. Concentration of NH3 ?.
    Temperature ?.

Stress
What happens?
29
Exothermic Reaction
  • Energy is released It flows from system to
    environment. Temperature of environment
    increases.

30
Endothermic Reaction
  • Energy is absorbed It flows from environment to
    system. Temperature of environment drops.

31
Heat of reaction, ?H
  • Hproducts - Hreactants

32
The difference between the potential energy of
the products the potential energy of the
reactants?
  • Hproducts Hreactants or ?H

33
?H for exothermic rxn
  • ?H is negative. System has net loss in energy.

34
?H is negative?
  • Exothermic reaction. Products have less
    potential energy than reactants.

35
?H is positive?
  • Endothermic reaction. Products have more
    potential energy than reactants.

36
?H for endothermic rxn
  • ?H is positive. System has net gain in energy.

37
A B ? C D heat
  • Exothermic Reaction. Heat term is on product
    side.

38
A B heat ? C D
  • Endothermic Reaction. Heat term is on reactant
    side.

39
Which phase change is endothermic?
  1. Gas to liquid
  2. Gas to solid
  3. Solid to gas
  4. Liquid to solid

40
Which phase change is exothermic?
  1. Solid to gas
  2. Liquid to gas
  3. Solid to liquid
  4. Liquid to solid

41
A reaction occurs in water the temperature of
the water increases. Endo or Exo?
  • Exothermic

42
A reaction occurs in water the temperature of
the water decreases. Endo or Exo?
  • Endothermic

43
A B ? C D. ?H -45 kJ.
  • What is ?H for C D ? A B?
  • ?H 45 kJ

44
A B ? C D. ?H -45 kJ.
  • What is ?H for
  • 2A 2B ? 2C 2D?
  • ?H -90 kJ

45
Entropy
  • Degree of disorder or chaos in a system.

46
Entropy
  • The more degrees of freedom a system has, the
    higher the entropy.

47
S
  • Entropy

48
H
  • Enthalpy
  • or
  • Chemical Potential Energy

49
0 entropy?
  • A perfect crystal at 0K

50
?S
  • Change in entropy
  • Sproducts Sreactants

51
Which phase has the greatest entropy?
  • Gas phase the molecules have more ways of
    moving more places to be!

52
Which phase has the greatest entropy?
  • Sgas gtgt Sliquid gt Ssolid

53
Did the entropy increase or decrease?
  • NaCl(s) ? Na(aq) Cl-(aq)

Increase!
54
Did the entropy increase or decrease?
  • CO2(g) ? CO2(aq)

Decrease!
55
Did the entropy increase or decrease?
  • 2H2O(l) ? 2H2(g) O2(g)

Increase!
56
Spontaneous Process
  • Physical or Chemical change that occurs with no
    outside intervention. (Supplying activation
    energy does not count!)

57
Nature is lazy disorganized.
  • Nature favors
  • Negative value for ?H Net loss
  • Positive value for ?S Net gain

58
When will a change never occur?
  • When both factors go against nature
  • Positive value for ?H Net gain in energy.
  • Negative value for ?S Net loss in chaos

59
  • Endo starts low, ends high

Endo or Exo?
60
  • Exo starts high, ends low

Endo or Exo?
61
Activated Complex
  • Reactants

Products
Identify reactants, products, activated complex
62
  • Potential energy of reactants

Identify the arrow
63
  • Activation energy of forward rxn

Identify the arrow
64
  • Heat of reaction

Identify the arrow
65
  • Activation energy of reverse reaction

Identify the arrow
66
  • Potential energy of activated complex

Identify the arrow
67
  • Potential energy of products

Identify the arrow
68
Collision Theory
  • Effective collisions between reacting particles
    must occur for a reaction to take place.

69
Effective Collisions
  • Energetic
  • Favorable Orientation

70
Rate of reaction
  • The speed of the reaction. The faster it occurs,
    the greater the rate.

71
Breaking Bonds
  • Absorbs Energy

72
Making Bonds
  • Releases Energy

73
6 Factors that influence the rate of reaction
  • Nature of reactants (ionic or covalent)
  • Temperature
  • Concentration
  • Pressure (for gases)
  • Surface area (for heterogeneous reactions)
  • Presence of a catalyst

74
Raising the temperature increases the reaction
rate by
  • Increasing both the number of collisions and the
    efficiency of the collisions.

75
As the concentrations of the reactants ?, the
rate of rxn
  • increases

76
As the pressure on gas-phase reactants ?, the
rate of rxn
  • Increases.

77
Which 4.0-gram Zn sample will react faster with
acid, and why?
  1. Lump
  2. Bar
  3. Powdered
  4. Sheet metal

More surface area
78
How does a catalyst work?
  • Provides an alternate reaction pathway with a
    lower activation energy.

79
Does a catalyst change ?H?
  • NO.

80
Which reacts faster ions in solution or
covalent molecules?
  • Ions in solution.

81
Which reacts faster in water 1 cm3 of Na or 1
cm3 of Ca?
  • 1 cm3 of Na -
  • Nature of the metals

82
Which is usually slower, an organic reaction or
an inorganic reaction?
  • Organic, because organic particles contain
    covalent bonds.

83
  • Lowers the activation energy.

Effect of a catalyst?
84
  • Potential energy of reactants

Identify the arrow
85
  • Activation energy of forward rxn

Identify the arrow
86
  • Activation energy of reverse rxn

Identify the arrow
87
  • Potential energy of activated complex

Identify the arrow
88
  • Heat of reaction

Identify the arrow
89
  • Potential energy of products

Identify the arrow
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