Chap 16 - 16 Chemical Kinetics The Rate of a Reaction...

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16 Chemical Kinetics
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2 The Rate of a Reaction Kinetics is the study of rates of chemical reactions and the mechanisms by which they occur. The reaction rate is the increase in concentration of a product per unit time or decrease in concentration of a reactant per unit time. A reaction mechanism is the series of molecular steps by which a reaction occurs.
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3 The Rate of a Reaction Kinetics (Chapter 16) determines how quickly a reaction occurs. Thermodynamics (Chapter 15) determines if a reaction can occur. Some reactions that are thermodynamically feasible are kinetically so slow as to be imperceptible.
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4 The Rate of a Reaction ( ) ( ) ( ) ( ) OUS INSTANTANE kJ -79 = G O H OH + H SLOW VERY kJ 396 G CO O C o 298 ) ( 2 - aq + o g 2 g 2 diamond = +
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5 The Rate of a Reaction Consider the hypothetical reaction: aA (g) + bB (g) cC (g) + dD (g) Equimolar amounts of reactants, A and B, will be consumed while products, C and D, will be formed as indicated in this graph:
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6 aA (g) + bB (g) cC (g) + dD (g) 0 0.2 0.4 0.6 0.8 1 1.2 0 50 100 150 200 250 300 350 Time Concentrations of Reactants & Products [A] & [B] [C] & [D] [ ] is the symbol for the concentration of in M ( mol/L). Note that the reaction does not go entirely to completion: the [A] and [B] > 0 plus the [C] and [D] < 1.
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7 The Rate of Reaction Reaction rates are the rates at which reactants disappear or products appear. This movie is an illustration of a reaction rate.
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8 The Rate of Reaction Mathematically, the rate of a reaction can be written as: [ ] [ ] [ ] [ ] t d D + t c C + or t b B - t a A - = Rate = =
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9 The Rate of Reaction The rate of a simple one-step reaction is directly proportional to the concentration of the reacting substance. [A] is the concentration of A in molarity or moles/L. k is the specific rate constant. [ ] [ ] A = Rate or A C + B A (g) (g) (g) k
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10 The Rate of Reaction For a simple expression like Rate = k[A]. If the initial concentration of A is doubled, the initial rate of reaction is doubled. If the initial concentration of A is halved the initial rate of reaction is cut in half.
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11 The Rate of Reaction For a simple expression like Rate = k[A], we said the initial concentration of A is doubled, the initial rate of reaction is doubled. If the reaction is proceeding twice as fast, the amount of time required for the reaction to reach equilibrium would be _____________. A. The same as the initial time. B. Twice the initial time. C. Half the initial time.
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12 The Rate of Reaction If more than one reactant molecule appears in the equation for a one-step reaction, we can experimentally determine that the reaction rate is proportional to the molar concentration of the reactant raised to the power of the number of molecules involved in the reaction. ( ) ( ) ( ) [ ] [ ] 2 2 g g g X k = Rate or X Z + Y X 2
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13 The Rate of Reaction Rate Law Expressions must be determined experimentally .
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This note was uploaded on 09/18/2010 for the course CHEM 1212 taught by Professor Suggs during the Fall '08 term at University of Georgia Athens.

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Chap 16 - 16 Chemical Kinetics The Rate of a Reaction...

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