Tài liệu Chemical Kinetics pdf

Chemical Kinetics The area of chemistry that concerns reaction rates. Reaction Rate Change in concentration (conc) of a reactant or product per unit time. Rate = conc of A at time conc of A at time 2 1 2 1 t t t t − − = ∆ ∆ A t 12_291 0.0003 70s O 2 0.0025 0.005 0.0075 0.0100 0.0006 70s 0.0026 110 s NO 2 NO 50 100 150 200 250 300 350 400 Concentrations (mol/L) Time (s) ∆ [NO 2 ] ∆ t 12_1575 Time Time (a) (b) (c) Rate Laws Rate = k[NO 2 ] n k = rate constant n = rate order Types of Rate Laws Differential Rate Law: expresses how rate depends on concentration. Integrated Rate Law: expresses how concentration depends on time. C 4 H 9 Cl + H 2 O → C 4 H 9 OH + HCl Method of Initial Rates Initial Rate: the “instantaneous rate” just after the reaction begins. The initial rate is determined in several experiments using different initial concentrations. NH 4 + (aq) + NO 2 - (aq) → N 2 (g) 2H 2 O(l) Overall Reaction Order Sum of the order of each component in the rate law. rate = k[H 2 SeO 3 ][H + ] 2 [I − ] 3 The overall reaction order is 1 + 2 + 3 = 6. [...]... [A]0 1 versus t [A] Slope = -k Slope = -k Rate law Integrated rate law Half-life t1/2 = [A]0 2k t1/2 = 0.693 k Slope = k t1/2 = 1 k[A]0 Reaction Mechanism - The series of steps by which a chemical reaction occurs - A chemical equation does not tell us how reactants become products - it is a summary of the overall process Reaction Mechanism (continued) - The reaction O3 + O → 2O2 has several steps in... determine integrated rate law, often graphically 6 For several reactants: choose conditions under which only one reactant varies significantly (pseudo n-order conditions) 12_06T Table 12.6 Summary of the Kinetics for Reactions of the Type aA → Products That Are Zero, First, or Second Order in [A] Order Zero First Second Rate = k Rate = k[A] [A] = -kt + [A]0 ln[A] = -kt + ln[A]0 Plot needed to give a straight . Chemical Kinetics The area of chemistry that concerns reaction rates. Reaction