Lecture+O

# Lecture+O - Ch 14 Recap Kinetics The rate of a simple...

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Ch 14 – Recap Kinetics The rate of a simple reaction rate = Δ [A] Δ t = Δ [B] Δ t A B But rate changes as the concentrations of reactants and products change! For a general reaction, a normalized rate can be obtained: aA + bB cC + dD predicts stoichiometric changes rate = Δ [A] Δ t 1 a Δ [B] Δ t 1 b = = Δ [C] Δ t 1 c = Δ [D] Δ t 1 d The rate law expresses the concentration dependence quantitatively. rate = k [A] x [B] y

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Δ [A] Δ t dA dt lim Δ t 0 rate = Solving the resulting rate expressions for various types of order gives unique solutions that can be used to identify the order of a reaction in one reagent = k [A] 0 = k 0 order integrated rate law rate = d[A] dt 1 a dA = ( ak) dt 1 st order integrated rate law d[A] [A] = ( ak) dt = k [A] rate = d[A] dt 1 a 2 nd order integrated rate law = k [A] 2 rate = d[A] dt 1 a d[A] [A] 2 = ( ak) dt Ch 14 – Recap Kinetics The instantaneous rate yields graphs characteristic of reaction order
Ch 14 – Recap Kinetics Important results from the integrated rate laws for the reaction aA products: Order Int. rate law t ½ linear plot? slope intercept 0 1 2 [A] t = [A] 0 akt [A] 0 2ak [A] vs t ak [A] 0 ln [A] t = ln [A] 0 akt *OR* [A] t = [A] 0 e akt 0.693 ak ln [A] vs t ak ln [A] 0 1 [A] t = 1 [A] 0 + akt 1 ak[A] 0 1 [A] vs t ak 1 [A] 0 Most problems involving integrated rate laws will involve determining from experimental data (usually a plot) what order is being followed, then applying the correct equations once the order is determined (“plug ‘n chug”).

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Ch 14 – Recap Kinetics Practice problem #43 Radioactive elements follow first-order kinetics as they decay to stable isotopes. The decay of 32 P has a half-life of 14.3 days. Using this information, answer the following questions. a) Determine the rate constant for the decay. Since 32 P uses first order kinetics, we know what integrated rate equations to use. t ½ = 0.693 ak with a = 1 k = 0.693 t ½ 0.693 14.3 = = 0.048 days 1 Why is a = 1? Because radioactive decay is not a chemical reaction- it’s a nuclear reaction – one elemental atom at a time
The Atom Isotope numbering Orbiting electrons protons neutrons X A Z Mass number Atomic number Element symbol = number of protons + number of neutrons = number of protons Ch 15.3 – Nuclear Chemistry

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235 92 U 238 92 For example, there are many isotopes of uranium: Isotopes of any particular element contain the same number of protons , but different numbers of neutrons . A
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## This note was uploaded on 11/04/2009 for the course CHEM Chem 1C taught by Professor Farmer during the Spring '09 term at UCL.

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Lecture+O - Ch 14 Recap Kinetics The rate of a simple...

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