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Published byAbel Strother Modified over 2 years ago

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Rate Law Learning Goals: I will be able to write a rate law equation using a table of data and calculate rate constants.I will become familiar with reaction mechanisms and how they relate to the rate law

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Rate Law Equation Equation used to connect the rate of reaction to the concentration([ ]) of its reactants (at a give T and P). Rate Law Equation Equation that shows the relationship between rate (r), rate constant (k), initial concentrations of reactants ([X] and [Y]), and the orders of reaction (m and n)

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Rate Law Equation For the reaction: 2 X + 2Y 2XY Rate Law Equation: Rate Constant -unique for every rxn -determined experimentally -varies with T so needs to be kept constant in each trial Order of Reaction -describes the exponents in the rate law equation -related to the particular reactant it is associated with -not related to the coefficients in the reaction equation Total Order of Reaction -sum of the individual orders of reaction for each reactant

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For the reaction equation:2X + 2B + 3C products [X] 1 If the initial [X] is doubled, rate will: If the initial [X] is tripled, rate will: [Y] 2 If the initial [Y] is doubled, the rate will: If the initial [Y] is tripled, rate will: [Z] 0 If the initial [Z] is doubled, rate will: If the initial [Z] is tripled, rate will: Reactant Order double triple quadruple 3^2 = 9 No effect

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Reactant Order Eg. NO 2 is the first order reactant (exponent 1) NO 2 is the first order reactant (exponent 1) O 2 is the second order reactant (exponent 2) O 2 is the second order reactant (exponent 2) What is the overall order of reaction?

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Initial Rate Instantaneous rate determined just after the reaction begins (just after t=0) Used to find the rate law equation for a reaction Use different concentrations of reactants to find the effect on the initial rate

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Example: RunInitial [NO(g)] mol/L Initial [H 2(g) ] mol/L Initial rate mol/L. s x x x Initial rates from three investigations for the reaction at 800 degrees Celsius represented by: 2NO(g) + 2H 2 (g) N 2 (g) + 2H 2 O (g) Find the rate law equation for the reaction above

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Units of k The order of a reaction can also be determine from the units of the rate constant. Rate is always measured in mol/(L. s). Therefore, a first order reaction has the unit of s -1 because: rate= k[A] mol = k x mol L. s L Total Reaction OrderUnits of k 0mol/(L. s) 11/s or s.1 2L/(mol. s) 3L 2 /mol 2. s)

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Example 2: The initial rate for the following reaction is 3.2x10 mol/(L.s) BrO Br - + 6H + 3Br 2 + H 2 0 The initial concentration of bromate is 0.10mol/L, hydrogen ion is 0.20mol/L, bromide is 0.10mol/L, and hydrogen ion is 0.20mol/L. It is first order with respect to bromate, first order with respect to bromide, and second order with respect to hydrogen ion. Find the rate constant, k, and the rate law expression.

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Example 3: For the reaction H 2 O 2 + 3I - + 2H + I H 2 O and the data shown below, determine the rate law equation.

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