Lecture 28 : Elementary Reactions and Reaction Mechanisms
28.6
Problems
28.1)
The Michaelis constant kM for an enzyme reaction is 0.04M. When the initial substarte concentration is 0.2 M, the reaction rate is 1.2 * 10 -3 Ms -1 ( M = mol / lit). How can you maximize the rate of enzymolysis? Under what conditions is the rate of the reaction half its value?
28.2)
A mechanism for the decomposition of propane is
C3H 8 CH3 + CH3
CH3- C3H8 CH4 + C3H7
C3H7 C2H4 + CH3
CH3 + CH3 C2H6
Using the steady state approximation find the expression for the formation of CH4
28.3)
The decomposition of N2O5 (g)
2 NO2 (g) + O2 (g) is accounted by the mechanism given below
N2 O5 NO2 + NO3
NO2 + NO3 NO +NO+ O2
NO + N2O5 3 NO2
Find an expression for the rate of production of O2
28.4)
There are two mechanisms for the reaction between H2 and I2. In the molecular mechanism, the reaction is of second order, i.e., d [HI] / dt = km [H2] [I2]. In the atomic mechanism, I - participates, i.e.,
I2 + M 2 I + M ; H2 + I + I
2 HI
Using the steady state approximation for I obtain the total rate of production of HI.
28.5)
The formation of phosgene [ COCl2 (g)] from CO(g) and Cl2(g) can occur by two mechanisms as shown below
a)
Cl2 2 Cl (equilibrium constant K1)
Cl + CO
COCl ( k2 )
COCl + Cl
COCl2
b)
Cl2 2 Cl (K1)
Cl + Cl2
Cl3 (K3)
Cl3+ CO
COCl2 + Cl
For each mechanism, derive the expression for d [ COCl2] / dt. How will you distinguish between the two mechanisms?
28.6)
The reaction between I - and ClO - is found to have the following mechanism
ClO- + H2O
HClO + OH - (Equilibrium const K1)
HClO + I- HIO + Cl-
HIO + OH- = IO- + H2O (K3)
Show that
d [ Cl -] / dt = { K2 K1 [ ClO -] [ I - ] - k-2 K -13 [ O - ] [ Cl - ] } / [ OH -]
CH3 + CH3 
CH4 + C3H7 
C2H4 + CH3
C2H6 
2 NO2 (g) + O2 (g) is accounted by the mechanism given below 
NO2 + NO3
NO +NO+ O2
3 NO2
2 I + M ; H2 + I + I
2 HI 
2 Cl (equilibrium constant K1) 
COCl ( k
COCl
2 Cl (K1) 
Cl3 (K3) 
COCl2 + Cl 
HClO + OH - (Equilibrium const K1) 
HIO + Cl-
C2 H5 Cl (g) 
2H2O + O2
2 HBr 
