Presentation on theme: "Rate Law Learning Goals:"— Presentation transcript:
1 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 lawRate Law
2 Rate Law EquationEquation used to connect the rate of reaction to the concentration([ ]) of its reactants (at a give T and P).Rate Law EquationEquation 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)
3 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 equationRate Constant-unique for every rxn-determined experimentally-varies with T so needs to be kept constant in each trialTotal Order of Reaction-sum of the individual orders of reaction for each reactant
4 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]2If the initial [Y] is doubled, the rate will:If the initial [Y] is tripled, rate will:[Z]0If the initial [Z] is doubled, rate will:If the initial [Z] is tripled, rate will:doubletriplequadruple3^2 = 9No effectNo effect
5 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
6 Initial RateInstantaneous rate determined just after the reaction begins (just after t=0)Used to find the rate law equation for a reactionUse different concentrations of reactants to find the effect on the initial rate
7 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 aboveRunInitial [NO(g)] mol/LInitial [H2(g)] mol/LInitial rate mol/L.s10.4000.1001.10 x 10-520.2002.20 x 10-530.8008.80 x 10-5
8 Units of kThe 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 molL.s LTotal Reaction OrderUnits of kmol/(L.s)11/s or s.12L/(mol.s)3L2/mol2.s)
9 Example 2:The initial rate for the following reaction is 3.2x10 mol/(L.s)BrO3- + 5Br- + 6H+ 3Br2 + H20The 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.
10 Example 3:For the reaction H2O2 + 3I- + 2H+ I3- + 2H2O and the data shown below, determine the rate law equation.