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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 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 Rate Law Equation: For the reaction: 2X + 2Y 2XY**

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 Rate Constant -unique for every rxn -determined experimentally -varies with T so needs to be kept constant in each trial Total Order of Reaction -sum of the individual orders of reaction for each reactant

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**Reactant Order 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: double triple quadruple 3^2 = 9 No effect No effect

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**Reactant Order 3 1+2 Eg. What is the overall order of reaction?**

NO2 is the first order reactant (exponent 1) O2 is the second order reactant (exponent 2) What is the overall order of reaction? 3 1+2

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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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**Find the rate law equation for the reaction above**

Example: Initial rates from three investigations for the reaction at 800 degrees Celsius represented by: 2NO(g) + 2H2(g) N2 (g) + 2H2O (g) Find the rate law equation for the reaction above Run Initial [NO(g)] mol/L Initial [H2(g)] mol/L Initial rate mol/L.s 1 0.400 0.100 1.10 x 10-5 2 0.200 2.20 x 10-5 3 0.800 8.80 x 10-5

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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 Order Units of k mol/(L.s) 1 1/s or s.1 2 L/(mol.s) 3 L2/mol2.s)

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Example 2: The initial rate for the following reaction is 3.2x10 mol/(L.s) BrO3- + 5Br- + 6H+ 3Br2 + H20 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 H2O2 + 3I- + 2H+ I3- + 2H2O and the data shown below, determine the rate law equation.

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Chapter 13: Chemical Kinetics CHE 124: General Chemistry II Dr. Jerome Williams, Ph.D. Saint Leo University.

Chapter 13: Chemical Kinetics CHE 124: General Chemistry II Dr. Jerome Williams, Ph.D. Saint Leo University.

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