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Kinetics

Kinetics. A study of the rate of change (reaction rates/speeds) of a chemical reaction Factors that affect reaction rate: The nature of the reactants The surface area of the reactants The temperature Adding a catalyst Adding an inhibitor Increasing the concentration of the reactants***.

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Kinetics

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  1. Kinetics • A study of the rate of change (reaction rates/speeds) of a chemical reaction • Factors that affect reaction rate: • The nature of the reactants • The surface area of the reactants • The temperature • Adding a catalyst • Adding an inhibitor • Increasing the concentration of the reactants***

  2. ***Concentration has the greatest affect on the reaction rate • The rate of change of a reaction is dependent on the concentration, the time, and the stoichiometry of the reaction EX: 4PH3(g)  P4(g) + 6H2(g) If 0.0048 mol PH3 is consumed in a 2.0 L container each second of reaction, what are the rates of production of P4 and H2 in this experiment?

  3. Rate Laws • Used to determine the way concentration affects the rate of the reaction • A + B  C rate = k[A]x[B]y • Based upon the rate of disappearance of the REACTANTS • k is the rate constant • k, x, and y all MUST be determined experimentally

  4. Use the following data to determine the rate law for the equation A + B  C

  5. Points about the Rate Law • k and the exponents are determined EXPERIMENTALLY – they are NOT based upon the coefficients of the reaction • k is specific to each reaction • k changes with temperature • Units of k depend upon the rate law itself and vary from reaction to reaction • k does not change with time • k IS dependent on the presence of a catalyst • The overall reaction order is the sum of the exponents of the rate law

  6. Reaction Order • Based upon the exponents of each substance in the rate law • Will use the reaction order to help determine the integrated rate law

  7. Integrated Rate Law • Allows the concentration of an amount of substance to be determined after some time has passed • Very useful in ½ life determinations • Based upon reaction orders

  8. Collision Theory In order for a chemical reaction to take place, reactants must collide with 1. proper orientation 2. enough energy for the reaction to occur

  9. 1. Proper Orientation

  10. 2. Correct amount of energy

  11. Arrhenius Equation: k = Ae(-Ea/RT) ln k = -Ea+ ln A RT To compare the reaction rate at two different temperatures: lnk2= -Ea1 - 1 k1 R T2-T1

  12. Catalyst • Does not affect anything other than the RATE of the reaction – it is not consumed as a reactant • Lowers the activation energy of a reaction • Transition metals make good catalyst

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