CHEM 135 1st Edition Lecture 13 Outline of Last Lecture I Factors affecting the rate of a reaction a Concentration b Temperature c Surface area II Demo observations a Glow sticks b Blue solution c Corn starch Outline of Current Lecture I Activation in a chemical reaction a Definition b Arrhenius equation c Examples II Reaction mechanism and reaction intermediate a Unimolecular b Bimolecular c Termolecular III Rate determining step and rate law a Example Current Lecture Activation energy in a chemical reaction Ea Lower the activation energy faster the rate of reaction REMEMBER frequent collisions energetic collision correct orientation product Arrhenius equation Takes into account all factors that affect the rate of a reaction k Ae E a RT 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 k rate constant Ae Arrhenius factor collision frequency and orientation factor R gas constant T temperature in kelvin Ea energy barrier to be surmounted in going from reactants to products ln The Arrhenius equation has two derivatives Ea 1 ln k ln A R T k2 E a 1 1 k1 R T 1 T 2 Ex If the activation energy for a given compound is found to be 42 0 kJ mol with a frequency factor of 8 0x1010 s 1 what is the rate constant for this reaction at 298K Given Ea 42 0 kJ mol A 8 0x1010 s 1 T 298K R 0 008314 kJ mol Ea 1 ln A R T 42 1 ln k ln 8 0 1010 0 008314 298 ln k ln k 8 15 k e 8 15 k 3 5x103 s 1 Reaction Mechanism and Reaction Intermediate Unimolecular A product rate k A 1 Bimolecular 2A product rate k A 2 Termolecular A B product rate k A B 1 3A product rate k A 3 A B C product rate k A B 1 C 1 Reaction intermediates appear in the elementary steps but not in the final balanced overall reaction Ex Overall reaction NO2 CO NO CO2 Elementary Steps 1 NO2 NO2 NO3 NO 2 NO3 CO NO2 CO2 Rate k NO3 CO2 1 Intermediate NO3 consumed element Ex H2 2ICl 2HCl I2 rate k H2 m ICl n 1 H2 ICl HCl HI rate k H2 1 ICl 1 bimolecular 2 HI ICl HCl I2 rate k HI 1 ICl 1 bimolecular H2 2ICl 2HCl I2 Intermediate HI Rate Determining Step Ex Rate determining step slow step determines the rate law of the overall reaction NO2 CO NO CO Rateabs k NO2 2 1 NO2 NO2 NO3 NO Rate k NO2 2 slow 2 NO3 CO NO2 CO2 Rate k NO3 CO fast Rate law of slow step rate law of overall reaction