Methane CH4 is present in the atmosphere due to a variety of natural and anthrop
ID: 858498 • Letter: M
Question
Methane CH4 is present in the atmosphere due to a variety of natural and anthropogenic sources. Isoprene C5H8 is a natural componenet of the atmosphere. The breakdown of both compounds begins with reaction with hydroxyl radical OH but whereas methane reacts with OH via H-atom abstraction, isoprene (which contains two C=C bonds) reacts via addition of *OH to one of the C=C bonds. The two reactions along with their respective rate laws and rate constants at 25 C are given below:
CH4+ OH--> CH3 (methyl radical)+H20
rate1=k1[CH4][OH]. k1=6.3x10^-15 molecule ^-1 cm ^3 s^-1
Isoprene+OH--> HO
rate (2)= k2[isoprene][OH] k2=1.0x10^-10 molecule^-1cm^3s^-1
Calculate the rates for the two reactions using the concentrations given. Which proceeds at a faster rate?
Explanation / Answer
1) CH4+ OH--> CH3 (methyl radical)+H20
rate1=k1[CH4][OH]. k1=6.3x10^-15 molecule ^-1 cm ^3 s^-1
2)Isoprene+OH--> HO
rate (2)= k2[isoprene][OH] k2=1.0x10^-10 molecule^-1cm^3s^-1
It is clear that both the reactions are second order reactions.So, for same initial concentration of reactants in both the reactions, the reaction with larger value of rate constant will move faster.
Hence , reaction (2) i.e )Isoprene+OH--> HO is faster