20080206 Chap13 Kinetics 1

20080206 Chap13 Kinetics 1 - Intro Chemistry II 030.102 -...

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Intro Chemistry II – 030.102 - Chapter 13 Spring, 2008 1 Chap. 13: Chemical Kinetics Powdered chalk (mostly calcium carbonate CaCO 3 ) reacts rapidly with dilute hydrochloric acid because it has a large total surface area. A stick of chalk has a much smaller surface area, so it reacts more slowly. Kinetics vs. Equilibrium Kinetics concerns the rate at which reactions occur. Equilibrium related to the extent a reaction proceeds if sufficient time is allowed. Consider the reaction: 5Fe 2+ ( aq ) + MnO 4 ( aq ) + 8H 3 O + ( aq ) 5Fe 3+ ( aq ) + Mn 2+ ( aq ) + 12H 2 O( l ) Ratio of concentrations at equilibrium can be determined from Gibbs free energy change, or voltage of galvanic cell. More difficult to determine how reaction proceeds from initial conditions to equilibrium.
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Intro Chemistry II – 030.102 - Chapter 13 Spring, 2008 2 Kinetics More difficult to determine how reaction proceeds from initial conditions to equilibrium. 5Fe 2+ ( aq ) + MnO 4 ( aq ) + 8H 3 O + ( aq ) 5Fe 3+ ( aq ) + Mn 2+ ( aq ) + 12H 2 O( l ) Reaction does not proceed by simultaneous collision of five Fe 2+ ions and one MnO 4 ion with eight H 3 O + ions. Rather, reaction proceeds through a series of elementary reactions, for example, Fe 2+ + MnO 4 Fe 3+ + MnO 4 2– MnO 4 2– + H 3 O + HMnO 4 + H 2 O HMnO 4 + Fe 2+ HMnO 4 2– + Fe 3+ etc. The set of such steps constitutes the reaction mechanism for the overall reaction. Chemical Kinetics: Topics to be Covered The speed of a reaction depends on many factors, for example concentrations, temperature, physical form of reagents, etc. Questions to be asked about the kinetics (rates) of reactions:
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20080206 Chap13 Kinetics 1 - Intro Chemistry II 030.102 -...

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