8/31/20091Chapter 12Chemical Kinetics12.1 Kinetics`The study of rates of reactions and reaction mechanisms (e.g., how fast a reaction will go and what steps it goes through)`What is rate?`Definition of reaction rate: the change in concentration of a reactant or product over change in time → Δ[A] / Δt12.1 Factors that Affect Rate`Concentrations`Temperature`Pressure`Catalysts`Surface area2NO2(g) →2NO (g) + O2(g)`How can rate be represented on a graph?`What happens to NO2over time? NO? O2?`How can their rates be expressed relative to each other?12.1 Graph of Reaction12.1 Relative Rates`Rate of NO2consumption = Rate of NO production = 2 × Rate of O2production`Thent]O[t2NO][t2]NO[22ΔΔ=ΔΔ=ΔΔ−t]O[2tNO][t]NO[22ΔΔ=ΔΔ=ΔΔ−
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8/31/2009212.1 Relative Rates`If NO2is disappearing at a rate of 4.2 x 10-5M/s, what is the rate of appearance of O2?t][Ot]NO[2122ΔΔ=ΔΔ⎟⎠⎞⎜⎝⎛−`Write the rates of the species in the following reaction:5Br-+ BrO3-+ 6H+→3Br2+ 2H2OGroup Quiz #1`According to the following unbalancedreaction, if the rate of appearance of oxygen gas is 4.00 x 10-2M/s, what is the rate of disappearance of KClO3(g)? KClO3(g) →KCl(g) + O2(g) 12.2 Rate Laws & Reaction Order`What happens to a chemical reaction over time? `Over time, the change in concentration will depend on the forward and reverse ireactions.`To simplify things, choose conditions before products become significant`This allows us to examine rates using onlyreactants12.2 Rate Laws`Reaction:`aA + bBÆProducts`Rate Law:nmBAkRate][=`k is Rate Constant`m& n are the order of reactants(NOT the coefficient); m & n must be determined experimentally!`Reaction Order = sum of reactant orders12.2 Rate Laws`Rate law of the decomposition reaction of NO2`Rate = k[NO2]m`k= rate constant`mis order of reactant(NOT the coefficient); m must be determined experimentally`Why do we want to determine the rate of a reaction?12.2 Types of Rate Laws`Differential Rate Law (or Rate Law)`rate depends on concentration`Integrated Rate Lawmk]NO[t][NORate22=ΔΔ−=`rate depends on time