H2 Chem - Reaction Kinetics

• gohby

  24 Aug 15, 17:41

  Hi UltimaOnline,

   

  I have a question concerning kinetics:

  
  

  http://img.photobucket.com/albums/v700/gohby/Chemistry/CJC%20Kinetics_zps9sn8h9zg.jpg

   

  My thoughts: Since S2O8 is present in a large excess, I can assume that it is a pseudo zero order reaction wrt S2O8 and thus the overall order of reaction is 1. Given that the overall order of reaction is 1, I can then use the formula half-life = ln2/k to get the half life of 3.5s. However the answer is D. (What is the relevance of the concentration of S2O8 being 0.5mol/dm³ btw?)

• UltimaOnline

  24 Aug 15, 17:53

  Originally posted by gohby:

  Hi UltimaOnline,

   

  I have a question concerning kinetics:

  
  

  http://img.photobucket.com/albums/v700/gohby/Chemistry/CJC%20Kinetics_zps9sn8h9zg.jpg

   

  My thoughts: Since S2O8 is present in a large excess, I can assume that it is a pseudo zero order reaction wrt S2O8 and thus the overall order of reaction is 1. Given that the overall order of reaction is 1, I can then use the formula half-life = ln2/k to get the half life of 3.5s. However the answer is D. (What is the relevance of the concentration of S2O8 being 0.5mol/dm³ btw?)

  
  My BedokFunland JC Solution :
  
  k' = k x [S2O8 2-] = 0.2 x 0.5 = 0.1
  
  t 1/2 = ln 2 / k' = ln 2 / 0.1 = 6.9315 s
  
  
  
  To better understand this question and solution, check out my BedokFunland JC questions here :
  
  http://www.infinity.usanethosting.com/Tuition/H2Chem_Kinetics_Can_Be_Tricky.jpg
  
  http://www.infinity.usanethosting.com/Tuition/H2Chem_Kinetics_calculate_rate_constant_k.jpg