Explanations 
Textbooks 
Flashcards 
91影视 AI 
Notes 
Study Plans 
Study Sets 
Find a degree 
Magazine Chapter 4: Q-4-54P (page 235)
When a small amount of iodine is added to a mixture of chlorine and methane, it prevents chlorination from occurring. Therefore, iodine is a free-radical inhibitor for this reaction. Calculate螖贬0values for the possible reactions of iodine with species present in the chlorination of methane and use these values to explain why iodine inhibits the reaction. (The I-Clbond-dissociation enthalpy is 211 kJ/molor 50 kcal/mol).
Short Answer
Bond dissociation energies are given below the bonds in kJ/mol and kcal/mol.
On comparing the second reaction in each pair, methyl radical reacting with chlorine is more exothermic than methyl radical reacting with iodine, but this does not explain how iodine prevents the chlorination reaction. On comparing the first reaction in each pair, we have the indication that, the chlorine atom reacting with iodine is very exothermic whereas chlorine atom reacting with methane is slightly endothermic. Chlorine atoms can be scavenged by iodine before they have a chance to react with methane. Without chlorine atoms, the reaction comes to a dead stop.
Step by step solution
Step-1. Calculation of ΔH0 values for the possible reactions of iodine with species present in the chlorination of methane:
Assuming that chlorine radicals are still generated in the initiation reaction and from the propagation steps, we will find out the enthalpy of formation values. Bond dissociation energies are given below the bonds in kJ/mol and kcal/mol. The values are calculated as follows when different radical species react and also with iodine. Values are calculated by subtracting the value of energy of the product from the reactant.
Calculation of 螖贬0 values
Step-2. Reason for iodine inhibiting the reaction:
On comparing the second reaction in each pair, methyl radical reacting with chlorine is more exothermic than methyl radical reacting with iodine, but this does not explain how iodine prevents the chlorination reaction. On comparing the first reaction in each pair, we have the indication that, the chlorine atom reacting with iodine is very exothermic whereas chlorine atom reacting with methane is slightly endothermic. Chlorine atoms can be scavenged by iodine before they have a chance to react with methane. Without chlorine atoms, the reaction comes to a dead stop.
Over 30 million students worldwide already upgrade their learning with 91影视!
