CHEM 108 1st Edition Lecture 12Chapter 14: Chemical Kinetics Continued:Factors Affecting Rate:- Concentration of reactants: Increased frequency of collisions, it is defined by rate law. - Energy of collisions: Energy needed to break bonds in reactants, allowing new bonds to form. - Orientation of colliding molecules.- Temperature: Increased temperature increases kinetic energy of molecules, molecular collisions. As temperature increases, the rate increases exponentially- Activation Energy (Ea): Minimum energy of molecular collisions required to break bondsin reactants, leading to formation of products. - These factors are all incorporated into rate constant k by Arrhenius Equation.Collision model:- Reactants react because they collide so if you increase collision rate, you increase reaction rate - Rate depends on frequency of collisions (Z) and probability of reaction upon collision (p)- Effect of concentration: o increase concentration, increase collision rate o increase collision rate, increase reaction rate- Effect of temperature: o increase temperature, increase kinetic energy o increase kinetic energy, increase velocity o increase velocity, increase collision rate o increase collision rate, increase reaction rateArrhenius Equation:- k= Ae-Ea/RT- k = rate constant - R = universal gas constant (in J/mol·K). - e = Euler’s number - Ea = Activation energy: minimum energy required to initiate a chemical reaction o Reaction pathway: path of least resistance in going from reactants to products- T = temperature (in Kelvin). - A= collisional frequency factor.o Includes frequency of collisions and an orientation factor. - Log form of Arrhenius Equation: ln k = (-Ea/R)(1/T) + ln A(y = mx + b form, where slope of the graph is (-Ea/R)- Reaction diagram: oActivation energy and kinetic theory:- Molecules have a distribution of speeds (or kinetic energy) - Some fraction of molecules will have kinetic energy great enough to react- If the reactants do not have enough energy to reach or go over the activation energy then the reaction won’t happen unless there is a catalyst or heat is added to the system.- Increase in fraction of collisions decreases theEa needed which causes an increase in k.- The smaller the Ea the larger the rate constant k- The larger the Ea the smaller the rate constant kEnergy Profiles:- Graphs showing changes in potential energy as a function of reaction progress.- Exothermic reaction:o- Endothermic
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