Physical Chem Notes-Practice 19

Physical Chem Notes-Practice 19 - Exercises to prepare for...

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Exercises to prepare for Feedback #4 A) A fast flash of light creates an initial concentration of electronically excited X (X # ), of 3.5 x 10 -6 Molar. The rate constant for X # X + h ν is 1 x 10 8 s -1 . What is the concentration of X # after 2.5 x 10 -8 seconds? B) Calculate the rate of reactions (1) and (2) at 298 K, assuming v 1 = k[F][CH 4 ] and v 2 = k[F][H 2 O] F + CH 4 HF + CH 3 k 1 = 1.6 x 10 –10 e -0.5 kcal/mole/RT cm 3 /(molecules sec) F + H 2 O HF + OH k 2 = 1.4 x 10 –10 cm 3 /(molecules sec) [CH 4 ] = 5 x 10 13 molecules/cm 3 [H 2 O] = 6 x 10 17 molecules/cm 3 [F] = 1 x 10 5 molecules/cm 3 Note 1 kcal/mole = 4184 J/mole C) A unimolecular reaction has a rate constant k(T) = A e -25 kcal/mole/RT sec -1 which equals 0.01 sec -1 at 298 K. What is the rate constant at 500 K? ------------------------------------------------------------------------------------------------------------ The numbers refer to the Exercises (not Problems) in Physical Chemistry , 8 th Edition
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