Chemical Kinetics All rates written as Δ conc Δ time or Δ [A] Δ t . Instantaneous rate is the slope of a concentration vs time plot and is shown by the differential equation: d[A] d t . Overall rates for forward reactions are shown as POSITIVE rates, therefore, all reactants (which have negative rate of change) must have their rates negated -d[A] d t . In general for the overall reation: a A + b B c C + d D overall rxn rate =-Δ [A] a Δ t =-Δ [B] b Δ t = + Δ [C] c Δ t = + Δ [D] d Δ t Note that each individual rate is divided by it’s coefficient in the balanced chemical equation. Half-life ( t 1/2 ) : The time it takes for the concentration to drop to one half its current value during the course of the reaction. Note that the “current value” is typically the initial starting value - but not always. Rate Laws for: A products Zero Order First Order Second Order rate = k rate = k [A] rate = k [A] 2 [A]0 − [A] t = kt ln[A]0 − ln[A] t = kt
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This note was uploaded on 11/29/2010 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.