01:160:162 Lecture Notes - Lecture 7: Reaction Rate Constant, Activation Energy, Propene

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25 Jul 2017

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High rate constant = faster rate of reaction. Arrhenius equation mathematical relationships between magnitude of rate constant and other factors (ex. temperature, energy, etc. ) ** k = ae (-ea / rt) ** K = rate constant (units depend on reaction order) A = frequency factor (same units as k) Ea = activation energy (j / mol) Minimum amount of e needed for a reaction to take place. E needed to overcome activation barrier of a reaction. Ex. fuse on a stick of dynamite. Ea is always positive since e must be supplied / absorbed for reaction to proceed. Numerically large ea leads to a slow reaction. Numerically small ea leads to a fast reaction. Plot of relative change in e as reaction proceeds from reactants to products. Ea and overall reaction enthalpies can be determined. Frequency factor number of times a reactant approaches an activation barrier per unit time. Approaching an activation barrier is not the same as overcoming it.

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In the collision model it is assumed that reactions occur as a result of collisions between molecules with the correct kinetic energy and orientation. The minimum energy required for a reaction to occur when molecules collide is called the activation energy, E_a. The number of collisions that are favorably oriented for a reaction is described by the frequency factor, A. The Arrhenius equation relates both of these factors to the rate constant, k. k = A middot e^-E_a/(R middot T) where R = 8.314 J/(mol middot K) and T is the temperature in kelvins. Based on the activation energies and frequency factors, rank the following reactions from fastest to slowest reaction rate, assuming they are all at the same temperature. Rank from fastest to slowest reaction rate. To rank items as equivalent, overlap them. Fraction of molecules The exponential term in the Arrhenius equation is equal to the fraction of molecules, f, with kinetic energy greater than or equal to the activation energy: f = e^-E_a/(R middot T) Most scientific calculators have an e^x function as the second function of the LN button. Part B A certain reaction with an activation energy of 145 kJ/mol was run at 495 K and again at 515 K. What is the ratio of f at the higher temperature to f at the lower temperature? Express your answer numerically using one significant figure. In the collision model it is assumed that reactions occur as a result of collisions between molecules with the correct kinetic energy and orientation. The minimum energy required for a reaction to occur when molecules collide is called the activation energy, E_a. The number of collisions that are favorably oriented for a reaction is described by the frequency factor, A. The Arrhenius equation relates both of these factors to the rate constant, k: k = A middot e^-E_a/(R middot T) where R = 8.314 J/(mol middot K) and T is the temperature in kelvins. Part A Based on the activation energies and frequency factors, rank the following reactions from fastest to slowest reaction rate, assuming they are all at the same temperature. Rank from fastest to slowest reaction rate. To rank items as equivalent, overlap them. Fraction of molecules The exponential term in the Arrhenius equation is equal to the fraction of molecules, f, with kinetic energy greater than or equal to the activation energy: f = e^E_a/(R middot T) Most scientific calculators have an e^x function as the second function of the LN button. Part B A certain reaction with an activation energy of 145 kJ/mol was run at 495 K and again at 515 K. What is the ratio of f at the higher temperature to f at the lower temperature? Express your answer numerically using one significant figure. In the collision model it is assumed that reactions occur as a result of collisions between molecules with the correct kinetic energy and orientation. The minimum energy required for a reaction to occur when molecules collide is called the activation energy, Ea. The number of collisions that are favorably oriented for a reaction is described by the frequency factor, A. The Arrhenius equation relates both of these factors to the rate constant, k: k = A middot e^-E_a/(R middot T) where R = 8.314 J/(mol middot K) and T is the temperature in kelvins. Fraction of molecules The exponential term in the Arrhenius equation is equal to the fraction of molecules, f, with kinetic energy greater than or equal to the activation energy: f = e^-E_a/(R middot T) Most scientific calculators have an e^x function as the second function of the LN button. Part B A certain reaction with an activation energy of 14 kJ/mol was run at 495 K and again at 515 K. What is the ratio of f at the higher temperature to f at the lower temperature? Express your answer numerically using one significant figure.

2. Using the Arrhenius equation, k = A e(^ -(Ea/RT)) a. Derive the equation of the plot of ln k vs. 1/T . b. Knowing that the value of the rate constant (k) for a certain reaction is 1.35ï´10ï4 sï1 at 35ï°C, and A= 2.6ï´1013 s-1, what is the activation energy? R= 8.314 J/K.mol c. Determine the half-life of the above reaction at the given temperature

01:160:162 Lecture Notes - Lecture 7: Reaction Rate Constant, Activation Energy, Propene

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