Please Pick Up  Activation Energy Problem Set

Activation Energy Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

6/12/2015 Activation Energy  Reading assignment: Zumdahl: Chapter  This lecture continues a discussion of the factors that affect the rate of a chemical reaction.  The topic of activation energy is introduced along with the Arrhenius equation.

Reaction Rate - dP A dt = k [A] n Factors that affect the rate of reaction concentration or pressure catalyst particle size temperature

Reaction Coordinate Diagram Collision Theory Energy  Reactants  Products EaEa HH For a chemical reaction to occur, the reactants must collide successfully with enough energy to overcome the activation energy (E a ). If the products are more stable than the reactants,  H < 0, the reaction is exothermic.

6/12/2015 Energy  Reactants  Products Reaction Coordinate Diagram Catalyst Why does the rate of reaction change when a catalyst is added? Why does  H for the reaction stay the same?

6/12/2015 The Rate Constant k = A e -E a /RT - dP N2O5N2O5 dt = k (P N2O5N2O5 )n)n

6/12/2015 Arrhenius Equation Factors Affecting the Rate of Reaction k = A e -E a /RT Rate constant Geometric factor Activation energy Temperature dependence (kelvin) Rewrite the Arrhenius equation in straight line form. The Arrhenius equation allows the rate of a reaction to be calculated at different temperatures.

Inverse Temperature (K -1 ) ln (Rate Constant) -E a /R Arrhenius Equation Linear Form

Arrhenius Equation The rate constant for a chemical reaction is 4.0 x s -1 at 280. K and 2.0 x s -1 at 300. K. What is the activation energy of this reaction? What rate constant would be expected at 320. K?

Boltzmann Distribution energy number of molecules average T 2 > T 1 The rate of many organic chemical reactions double with every 10 degree change in temperature.

Reaction Rates vary with Temperature If you run a fever of a 103 °F, how much “faster” is your body running, than at a normal temperature? The rate of many organic chemical reactions doubles with every 10 degree Celcius change in temperature around room temperature.