Chapt14_stu_10th_ed_07

Chapt14_stu_10th_ed_07 - REACTION RATE - rate at which...

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REACTION RATE - rate at which reactants are converted to products has units concentration/time molarity/sec M/sec
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concentration Rate = -------------------------- time conc. products = -------------------------- time [products] = ---------------------- time [ A] = molar concentration of A conc. reactants = - ----------------------- time [reactants] = - -------------------- time
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time c o n c e n t r a t i o n [H 2 ] H 2 + Cl 2 -----> 2 HCl RATE is the slope of the line in a concentration time plot. The rate of a reaction changes as the reaction proceeds. As the concentration of a reactant decreases, the rate of the reaction usually decreases. Initial rate: the rate at the start of the reaction.
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time c o n c e n t r a t i o n [HCl] [H 2 ] [Cl 2 ] H 2 + Cl 2 -----> 2 HCl
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- Reaction Rate = ------------------ [HCl] Reaction Rate = ------------------ 2 t - Reaction Rate = ---------------- H 2 + Cl 2 -----> 2 HCl
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General Case a A + b B ------------> c C + d D [C] [D] Rate = ------------- = -------------------- c t d t Positive - formation of products - [A] - [B] Rate = --------------- = ---------------- a t b t Negative - reactants being used up ∆ [product] Rate = ------------------ rxn coef x ∆t ∆ [reactant] = - ---------------------- rxn coef x ∆t
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Consider the reaction 4 NH 3 + 5 O 2 ---> 4 NO + 6 H 2 O. How does the rate of change of the other species compare with the rate of change of NH 3 ?
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Things Which Effect the Rate of a Reaction 1. The nature of the reactants 2. Concentration of reactants 3. Temperature 4. Presence of a catalyst
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Nature of the Reactants 1. size of the activation energy s the driving force in the reaction more later how well do the reactants want to react 2. for solids- particle size amount of surface area the more surface area - the faster the reaction
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Concentration Effects Expressed in term of the RATE LAW: The rate of a reaction is proportional to concentration of each reactant to some power. For the reaction: a A + b B ----> products Rate Law: Rate = k[A] x [B] y k = RATE CONSTANT - constant for a given reaction at a given temperature x & y - reaction ORDER
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REACTION ORDER The previous reaction would be said to be: x - order in A y - order in B x + y - order overall value of x or y 1 - first order 2- second order 3 - third order 0 - zero order (rate is independent of that reactant)
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UNITS OF k Depends on the rate law Rate = k[ ] x+y x+ y = overall reaction order Rate units = M / sec = M sec -1 k = rate/ [ ] x+y units of k = M sec -1 / M x+y = 1/ M x+y-1 sec = M -(x+y-1) /sec Example: Rate = k[A] 2 k = 1/ M sec = M -1 /sec -1 2
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Chapt14_stu_10th_ed_07 - REACTION RATE - rate at which...

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