chapter16Dec5 - 16-1Chapter 16: Chapter 16 Kinetics: Rates...

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Unformatted text preview: 16-1Chapter 16: Chapter 16 Kinetics: Rates and Mechanisms of Chemical Reactions16-2EXPECTED TOPICS FOR TEST/FINALKinetics: Rates and Mechanisms of Chemical Reactions16.7aFactors That Influence Reaction Rate16.2Expressing the Reaction Rate16.3The Rate Law and Its Components16.4Integrated Rate Laws: Concentration Changes over Time16.7Catalysis: Speeding Up a Chemical Reaction16.5The Effect of Temperature on Reaction Rate16.6Explaining the Effects of Concentration and Temperature16-3Factors That Influence Reaction RateUnder a specific set of conditions, every reaction has its owncharacteristic rate, which depends upon the chemical nature ofthe reactants.Four factors can be controlled during the reaction:1.Concentration - molecules must collide to react;2.Physical state - molecules must mix to collide;3.Temperature - molecules must collide with enough energy to react;4.The use of a catalyst.16-4Definitions:•All chemicals are measured in molarity •(moles solute/ Liters of solution). [chem] = mol/ L•Rate = mol/L•sec (always same units)•Rate = k [reactant A]x[reactant B]y[reactant C]z…•∆= final – initial. So for the reaction•A + B → C + D, •∆[A] is negative ∆[C] is positive as reaction proceeds•Rate is defined to be positive so Rate ∝- ∆[A] •Rate = k [A]x[B]y16-5Definitions:•k is a reaction rate constant (always positive, but units and values change with each reaction)•Reaction order (integral powers x,y, z, on prior slide)•Consider: A → B , Rate = k[A] First order in A , and k has units 1/sec •Consider: A + A → B , Rate = k[A]22nd order in A , and k has units L/mol*sec (how do you know?!)16-6Table 16.3 Units of the Rate Constant kfor Several Overall Reaction OrdersOverall Reaction OrderUnits of k(tin seconds)mol/L*s (or mol L-1s-1)11/s (or s-1)2L/mol*s (or L mol -1s-1)3L2/ mol2*s (or L2 mol-2s-1)16-7In general, for the reactionaA + bB cC + dDrate = 1a-= -∆[A]∆t1b∆[B]∆t1c∆[C]∆t= +1d∆[D]∆t= +The numerical value of the rate depends upon the substance that serves as the reference. The rest is relative to the balanced chemical equation.∆Assumes linear behavior!In this case-the stoichiometric coefficients ARE used (interested in total rate not just order)16-8Sample Problem 16.1PLAN:SOLUTION:Expressing Rate in Terms of Changes in Concentration with TimePROBLEM:Because it has a nonpolluting product (water vapor), hydrogen gas is used for fuel aboard the space shuttle and may be used by earthbound engines in the near future.2H2(g) + O2(g) 2H2O(g)(a) Express the rate in terms of changes in [H2], [O2], and [H2O] with time.(b) When [O2] is decreasing at 0.23 mol/L*s, at what rate is [H2O] increasing?Choose [O2] as a point of reference since its coefficient is 1. For every molecule of O2which disappears, 2 molecules of H2disappear and 2 molecules of H2O appear, so [O2] is disappearing at half the rate of change of H2and H2O....
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This note was uploaded on 10/16/2009 for the course CHEM 1035 at Virginia Tech.

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chapter16Dec5 - 16-1Chapter 16: Chapter 16 Kinetics: Rates...

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