ch302 notes ch15.2

# ch302 notes ch15.2 - CH302 Chapter 15 KINETICS The...

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CH302 Chapter 15 KINETICS The Integrated Rate Equation This relates time and concentration for chemical (and nuclear!) reactions. (What we do: write the rate expression replacing with d . Then rearrange, and integrate over all values of time, t.) From it we can predict an amount of product produced in a given amount of time. We can also calculate the half life of a reactant: the time taken for HALF of the original reactant to have reacted. (This is done by rearranging the integrated rate equation with respect to t and then finding the value of T when the concentration has dropped to half the original value.) We will only cover the integrated rate equation and half life for first, second and zeroth order reactions . Finding Reaction Order Graphically: Comparing each rate law to the generic line equation y = mx + c we can see what parameters to plot to "test" what the reaction order might be! The Integrated Rate Equation: 1 st Order: For a reaction that is 1 st order in the reactant and 1 st order overall. Very common in chemical reactions and in simple radioactive decay! Examples are: 2 N 2 O 5(g) 2 N 2 O 4(g) + O 2(g) 238 U 234 Th + 4 He The rate equation is: [] [] - 1 A kA d ⎟ = a t d The integrated rate equation is: [] [] k t a A A ln t 0 = [A] 0 = mol/L of A at time t=0. [A] = mol/L of A at time t. k = specific rate constant. t = time elapsed since beginning of reaction. a = stoichiometric coefficient of A in the balanced overall equation. First Order, Graphically Using this law of logarithms: ln (x/y) = ln x - ln y we get: [ ] [ ] k t a A ln A ln 0 = this can be rearranged into [] [ ] 0 A ln k t a A ln + = compare to b m y + = x y can be identified with ln[A] and plotted on the y-axis. A plot of ln[A] vs. t should be linear if the reaction

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ch302 notes ch15.2 - CH302 Chapter 15 KINETICS The...

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