CHEM 113 1st Edition Lecture 5 Current Lecture16.5: Theories of chemical kinetics- Collision Theory: The basis of the rate lawo The basic principle of the collision theory is that particles must collide in order toreact.o Why concentrations are multiplied in the rate law. An increase in the concentration of a reactant leads to a larger number of collisions, hence increasing the reaction rate. The number of collisions depends on the product of the numbers of reactant particles, not their sum.- Hence concentrations are multiplied, not added.- Figure 16.13 illustrates this well. The number of collisions per unit time, provides an upper limit on how fast a reaction can take place. - Temperature and the rate constanto Temperature has a dramatic effect on reaction rate. For many reactions, and increase of 10 degrees Celsius can double or triple the rate.o Experimental data shows that k increases exponentially as T increases.  This is expressed in the Arrhenius equation.-k = Ae-Ea/RT- k= rate constant- A= frequency factor- E subscript a= activation energy Higher T larger k increased rate- Activation energyo In order to be effective, collisions between particles must exceed a certain energythreshold.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o When particles collide effectively, they reach and activated state. The energy difference between the reactants and the activated state is the activation energyfor the reaction.o The lower that activation energy, the faster the reaction Smaller activation energy larger collision frequency larger k  increased rate- Temperature and collision energyo An increase in temperature causes an increase in the kinetic energy particles. This leads to more frequent collisions and reaction rate increases.o At a higher temperature, the fraction of collisions with sufficient energy equal to or greater than the activation energy increases. Therefore rate increases.  Note that not all collisions provide the same energy.- Calculating Activation Energyo Activation energy can be calculated from the Arrhenius equationo Using only one reading ln k = ln A- ((activation energy/R) * (1/T)o When data is available at two different temperatures ln(k2/k1)= (-activation energy/R) *((1/T2)-(1/T1))- Molecular structure and reaction rateo For a collision between particles to be effective, it must have both sufficient energy and the appropriate relative orientation between the reacting particles. The atoms that become the product are bonded and thus must make contact.o When looking at the Arrhenius equation, the A contains the molecular orientation and therefore is the frequency factor. This frequency factor can be described as the following- A= pZo p= orientation probability factor This term is specific for each reaction and is related to the structural complexity of the reactants - Single atoms are spherical and have p-values that are approximately 1.- More complicated molecules have p-values less than 1. o Z= collision frequency There may be only one relative orientation that may work for an effective collision.- Transition state theoryo An effective collision between particles leads to the formation of a transition state or activated complex.o The transition state is an instable species that contains partial bonds. It is a transitional species partway between reactants and products Transition states cannot be isolated.o The transition state exists at the point of maximum potential energy. The energy required to form the transition state is the activation energy. In the tiny fraction of collisions in which molecules are moving fast enough, their kinetic energies push them together with enough force to overcome the repulsions and surpass the activation