 The rate expression is an equation  Determined experimentally  Shows dependence of rate on concentrations of reactants  Rate is found whilst changing concentration of a reactant Rate Expression

Order of Reaction

Experimental Data

 If doubling concentration has no effect then zero order (w.r.t. that reactant)  If doubling concentration doubles rate then first order  If doubling concentration quadruples rate then it is second order  What are orders for A, B, and C on page 171?  Therfore what is rate expression? Order of Reaction

 Please read pages 170 to 173  Make any notes you need.  Then try questions 1 to 7 from page 173. Reading and Questions

 Most reactions occur in a number of steps  At each stage only two particles collide successfully  Intermediates therfore exist  Slowest step is the rate determing step Reaction Mechanism

Rate determing Step

Reaction Mechanism

Unimolecular step

Bimolecular

 See page 176, figure 618 Relating mechanism to Rate Expression

Activation Energy

Maxwell-Boltzmann distribution

 The Activation energy can be determined using an equation  The Arrhenius Equation  This shows the effect of temperature on the rate constant for a reaction Arrhenius Equation

The Arrhenius Equation

 The rate constant, k, depends exponentially on the temperature  This is why temperature has a large effect on reaction rate  Using logs and rearranging the equation….. Arrhenius

Arrhenius equation converted to…

 What is intercept ?  Gradient ?  Y and x axis ? Compare to y=mx + c

Ea can be determined graphically….

 So the activation energy can be found by measuring the rate at different temperatures, with all the other conditions unchanged and then plotting In(rate) against 1/T (in Kelvin) Finding Ea