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  • 1. REACTION RATEHow Fast Does the Reaction Go
    Irma
    Sesion #08
    JurusanKimia
    FakultasMatematikadanIlmuPengetahuanAlam
  • 2.
    • Mahasiswamemahami laju reaksi.
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
    2
  • 3. INDIKATOR
    Mendiskusikan faktor-faktor yang mempengaruhi laju reaksi
    Mendefinisikan konstanta laju, dan orde reaksi dengan detail
    Menghitung laju reaksi dan konstanta laju
    Menentukan orde reaksi
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
    3
  • 4. COLLISION THEORY
    In order to react molecules and atoms must touch each other.
    They must hit each other hard enough to react.
    Anything that increase these things will make the reaction faster.
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
    4
  • 5. Reactants
    Energy
    Products
    Reaction coordinate
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
    5
  • 6. Activation Energy - Minimum energy to make the reaction happen
    Reactants
    Energy
    Products
    Reaction coordinate
    6
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 7. Activated Complex or Transition State
    Reactants
    Energy
    Products
    Reaction coordinate
    7
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 8. Reactants
    Products
    Energy
    Overall energy change
    Reaction coordinate
    8
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 9. Things That Effect Rate
    • Temperature
    • 10. Higher temperature faster
    particles.
    • More and hardercollisions.
    • 11. Faster Reactions.
    9
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 12. Things That Effect Rate
    • Concentration
    • 13. More concentrated closer together the molecules.
    • 14. Collide more often.
    • 15. Faster reaction.
    10
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 16. Concentration
    11
    If we make one reactant more concentrated (like making a drink of orange squash more concentrated)
    There are moreparticles in the same volume to react
    So the reaction goes faster.
    There are less red particles in the same volume so there is less chance of a collision
    There are more red particles in the same volume so there is more chance of a collision so the reaction goes faster
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 17. Things that Effect Rate
    • Particle size
    • 18. Molecules can only collide at the surface.
    • 19. Smaller particles bigger surface area.
    • 20. Smaller particles faster reaction.
    • 21. Smallest possible is molecules or ions.
    • 22. Dissolving speeds up reactions.
    • 23. Getting two solids to react with each other is slow.
    12
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 24. Particle size - Surface area
    If we make the pieces of the reactants smaller we increase the number of particles on the surface which can react.
    This makes the reaction faster.
    13
    The particles on the surface can react
    When cut into smaller pieces the particles on the inside can react
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 25. Things that Effect Rate
    • Catalysts- substances that speed up a reaction without being used up.(enzyme).
    • 26. Speeds up reaction by giving the reaction a new path.
    • 27. The new path has a lower activation energy.
    • 28. More molecules have this energy.
    • 29. The reaction goes faster.
    • 30. Inhibitor- a substance that blocks a catalyst.
    14
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 31. Reactants
    Energy
    Products
    Reaction coordinate
    15
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 32. H
    H
    H
    H
    H
    H
    H
    H
    Catalysts
    Hydrogen bonds to surface of metal.
    Break H-H bonds
    Pt surface
    16
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 33. H
    H
    H
    H
    Pt surface
    Catalysts
    17
    H
    H
    C
    C
    H
    H
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 34. H
    H
    H
    Catalysts
    The double bond breaks and bonds to the catalyst.
    18
    H
    C
    C
    H
    H
    H
    H
    Pt surface
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 35. H
    H
    H
    H
    Catalysts
    The hydrogen atoms bond with the carbon
    19
    C
    C
    H
    H
    H
    H
    Pt surface
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 36. 20
    H
    H
    C
    C
    H
    H
    H
    H
    H
    H
    Catalysts
    Pt surface
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 37. Reaction Mechanism
    Elementary reaction- a reaction that happens in a single step.
    Reaction mechanism is a description of how the reaction really happens.
    It is a series of elementary reactions.
    The product of an elementary reaction is an intermediate.
    An intermediate is a product that immediately gets used in the next reaction.
    21
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 38. 22
    • This reaction takes place in three steps
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 39. First step is fast
    Low activation energy
    Ea
    23
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 40. Ea
    Second step is slow
    High activation energy
    24
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 41. Ea
    Third step is fast
    Low activation energy
    25
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 42. Second step is rate determining
    26
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 43. Intermediates are present
    27
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 44. Activated Complexes or Transition States
    28
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 45. Mechanisms and rates
    There is an activation energy for each elementary step.
    Slowest step (rate determining) must have the highest activation energy.
    29
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 46. THERMODYNAMICS
    Will a reaction happen?
    30
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 47. ENERGY
    Substances tend react to achieve the lowest energy state.
    Most chemical reactions are exothermic.
    Doesn’t work for things like ice melting.
    An ice cube must absorb heat to melt, but it melts anyway. Why?
    31
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 48. ENTROPY
    The degree of randomness or disorder.
    The first law of thermodynamics. The energy of the universe is constant.
    The second law of thermodynamics. The entropy of the universe increases in any change.
    Drop a box of marbles.
    Watch your room for a week.
    32
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 49. ENTROPY
    A solid has an orderly arrangement.
    A liquid has the molecules next to each other.
    A gas has molecules moving all over the place.
    33
    Entropy of a liquid
    Entropy of a solid
    Entropy of a gas
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 50. Entropy increases when...
    Reactions of solids produce gases or liquids, or liquids produce gases.
    A substance is divided into parts -so reactions with more reactants than products have an increase in entropy.
    the temperature is raised -because the random motion of the molecules is increased.
    a substance is dissolved.
    34
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 51. Entropy calculations
    There are tables of standard entropy.
    Standard entropy is the entropy at 25ºC and 1 atm pressure.
    Abbreviated Sº, measure in J/K.
    The change in entropy for a reaction is
    DSº= Sº(Products)-Sº(Reactants)
    Calculate DSº for this reaction
    CH4(g) + O2(g) ® CO2(g) + H2O(g)
    35
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 52. SPONTANEITY
    Will the reaction happen, and how can we make it?
    36
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 53. Spontaneous reaction
    Reactions that will happen.
    Nonspontaneous reactions don’t.
    Even if they do happen, we can’t say how fast.
    Two factors influence.
    Enthalpy (heat) and entropy(disorder).
    37
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 54. Two Factors
    Exothermic reactions tend to be spontaneous.
    Negative DH.
    Reactions where the entropy of the products is greater than reactants tend to be spontaneous.
    Positive DS.
    A change with positive DS and negative DH is always spontaneous.
    A change with negative DS and positive DH is never spontaneous.
    38
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 55. Other Possibilities
    Temperature affects entropy.
    Higher temperature, higher entropy.
    For an exothermic reaction with a decrease in entropy (like rusting).
    Spontaneous at low temperature.
    Nonspontaneous at high temperature.
    Entropy driven.
    39
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 56. Other Possibilities
    An endothermic reaction with an increase in entropy like melting ice.
    Spontaneous at high temperature.
    Nonspontaneous at low temperature.
    Enthalpy driven.
    40
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 57. Gibbs Free Energy
    The energy free to do work is the change in Gibbs free energy.
    DGº = DHº - TDSº (T must be in Kelvin)
    All spontaneous reactions release free energy.
    So DG <0 for a spontaneous reaction.
    41
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 58. -
    +
    -
    +
    +
    ?
    -
    -
    ?
    +
    -
    +
    DG=DH-TDS
    Spontaneous?
    DH
    DS
    DG
    At all Temperatures
    At high temperatures,
    “entropy driven”
    At low temperatures,
    “enthalpy driven”
    Not at any temperature,
    Reverse is spontaneous
    42
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 59. Problems
    Using the information, determine if the following changes are spontaneous at 25ºC.
    2H2S(g) + O2(g) ® 2H2O(l) + S(rhombic)
    At what temperature does it become spontaneous?
    43
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 60. 2H2S(g) + O2(g) ® 2H2O(l) + 2S
    From the information, we find Hf° for each component
    H2S = -20.1 kJ O2= 0 kJ
    H2O = -285.8 kJ S = 0 kJ
    Then Products - Reactants
    H = [2 (-285.8) - 0] - [2 (-20.1) + 1(0)]
    = -531.4 kJ
    44
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 61. 2H2S(g) + O2(g) ® 2H2O(l) + 2 S
    From Pg. 407 we find S for each component
    H2S = 205.6 J/K O2= 205.0 J/K
    H2O = 69.94 J/K S = 31.9 J/K
    Then Products - Reactants
    S= [2 (69.94) - 2(31.9) ] - [2 (205.6) + 205]
    = -412.5 J/K
    45
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 62. 2H2S(g) + O2(g) ® 2H2O(l) + 2 S
    G = H - T S
    G = -531.4 kJ - 298K (-412.5 J/K)
    G = -531.4 kJ - -123000 J
    G = -531.4 kJ - -123 kJ
    G = -408.4 kJ
    Spontaneous
    Exergonic- it releases free energy.
    At what temperature does it become spontaneous?
    46
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 63. Spontaneous
    • It becomes spontaneous when G = 0
    • 64. That’s where it changes from positive to negative.
    • 65. Using 0 = H - T S and solving for T
    • 66. 0 - H = - T S
    • 67. = -T
    • 68. T = = =
    47
    -H
    S
    H
    S
    -531.4 kJ
    -412.5 J/K
    -531400 J
    -412.5 J/K
    = 1290 K
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 69. There’s Another Way
    There are tables of standard free energies of formation compounds
    DGºf is the free energy change in making a compound from its elements at 25º C and 1 atm.
    for an element DGºf = 0
    Look them up.
    DGº= DGºf(products) - DGºf(reactants)
    Check the last problems.
    48
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 70. 2H2S(g) + O2(g) ® 2H2O(l) + 2S
    From Pg. 414 we find Hf° for each component
    H2S = -33.02 kJ O2= 0 kJ
    H2O = -237.2 kJ S = 0 kJ
    Then Products - Reactants
    H = [2 (-237.2) - 2(0)] - [2 (-33.02) + 1(0)]
    = -408.4 kJ
    49
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 71. 50
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 72. Reversible Reactions
    Reactions are spontaneous if DG is negative.
    If DG is positive the reaction happens in the opposite direction.
    2H2(g) + O2(g) ® 2H2O(g) + energy
    2H2O(g) + energy ® 2H2(g) + O2(g)
    2H2(g) + O2(g) 2H2O(g) + energy
    51
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 73. Equilibrium
    When I first put reactants together the
    forward reaction starts.
    Since there are no products there is no reverse reaction.
    As the forward reaction proceeds the reactants are used up so the forward reaction slows.
    The products build up, and the reverse reaction speeds up.
    52
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 74. Equilibrium
    Eventually you reach a point where the reverse reaction is going as fast as the forward reaction.
    This is dynamic equilibrium.
    The rate of the forward reaction is equal to the rate of the reverse reaction.
    The concentration of products and reactants stays the same, but the reactions are still running.
    53
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 75. Equilibrium
    Equilibrium position- how much product and reactant there are at equilibrium.
    Shown with the double arrow.
    Reactants are favored
    Products are favored
    Catalysts speed up both the forward and reverse reactions so don’t affect equilibrium position.
    54
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 76. Measuring equilibrium
    At equilibrium the concentrations of products and reactants are constant.
    We can write a constant that will tell us where the equilibrium position is.
    Keq equilibrium constant
    Keq = [Products]coefficients [Reactants]coefficients
    Square brackets [ ] means concentration in molarity (moles/liter)
    55
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 77. Writing Equilibrium Expressions
    General equation aA + bB cC + dD
    Keq [C]c [D]d [A]a [B]b
    Write the equilibrium expressions for the following reactions.
    3H2(g) + N2(g) 2NH3(g)
    2H2O(g) 2H2(g) + O2(g)
    56
    =
    06/01/2011
    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 78. Calculating Equilibrium
    Keq is the equilibrium constant, it is only effected by temperature.
    Calculate the equilibrium constant for the following reaction. 3H2(g) + N2(g) 2NH3(g) if at
    25ºC there 0.15 mol of N2 , 0.25 mol of NH3 , and 0.10 mol of H2 in a 2.0 L container.
    57
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 79. What it tells us
    If Keq > 1 Products are favored
    If Keq < 1 Reactants are favored
    58
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 80. LeChâtelier’s Principle
    Regaining Equilibrium
    59
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 81. LeChâtelier’s Principle
    If something is changed in a system at equilibrium, the system will respond to relieve the stress.
    Three types of stress are applied.
    60
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 82. Changing Concentration
    If you add reactants (or increase their concentration).
    The forward reaction will speed up.
    More product will form.
    Equilibrium “Shifts to the right”
    Reactants ® products
    61
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 83. Changing Concentration
    If you add products (or increase their concentration).
    The reverse reaction will speed up.
    More reactant will form.
    Equilibrium “Shifts to the left”
    Reactants ¬ products
    62
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 84. Changing Concentration
    If you remove products (or decrease their concentration).
    The forward reaction will speed up.
    More product will form.
    Equilibrium “Shifts to the right”
    Reactants ® products
    63
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 85. Changing Concentration
    If you remove reactants (or decrease their concentration).
    The reverse reaction will speed up.
    More reactant will form.
    Equilibrium “Shifts to the left”.
    Reactants ¬ products
    Used to control how much yield you get from a chemical reaction.
    64
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 86. Changing Temperature
    Reactions either require or release heat.
    Endothermic reactions go faster at higher temperature.
    Exothermic go faster at lower temperatures.
    All reversible reactions will be exothermic one way and endothermic the other.
    65
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 87. Changing Temperature
    As you raise the temperature the reaction proceeds in the endothermic direction.
    As you lower the temperature the reaction proceeds in the exothermic direction.
    Reactants + heat ® Products at high T
    Reactants + heat ¬ Products at low T
    66
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 88. Changes in Pressure
    As the pressure increases the reaction will shift in the direction of the least gases.
    At high pressure 2H2(g) + O2(g) ® 2 H2O(g)
    At low pressure 2H2(g) + O2(g) ¬ 2 H2O(g)
    67
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • 89. HAPPY
    STUDY
    68
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    © 2010 Universitas Negeri Jakarta | www.unj.ac.id |