In: Chemistry
The decomposition of CCl3CHS can be considered to be the following. (1) CH3CHS CH3 + CHS (2) CH3 + CH3CHS CH4 + CH3CS (3) CH3CS CS + CH3 (4) 2CH3 C2H6 The CHS reacts to form very minor amounts of other moeities. (i) Determine the initiation, propagation and termination steps. (ii) Determine the overall reaction neglecting the minor species cited. (iii) Determine r for the reaction where k = k2(k1/2k4)1/2.
The reactions are
(i)
CH3CHS --> CH3 + CHS.......(initiation) (let rate constant =K1]
CH3 + CH3CHS --> CH4 + CH3CS ............(propagation) (rate constant = K2)
CH3CS --> CS + CH3............(propagation) (rate constant = K3)
2CH3 --> C2H6..........(termination) (rate constant = K4)
(ii) 2CH3CHS --> C2H6 + H2S (overall reaction)
(iii) Rate of reaction = d[C2H6] / dt = K4[CH3]^2 ......(1)
Applying Steady state approximation to CH3
d[CH3 ] / dt = 0 = K1[CH3CHS] - K2[CH3][CH3CHS] + K3 [CH3CS] - 2K4[CH3]^2 ...(2)
Applying SSA to CH3CS
d[CH3CS ] / dt = 0 = K2[CH3][CH3CHS] -K3 [CH3CS] = 0 ....................(3)
Add (2) and (3)
K1[CH3CHS] - 2K4[CH3]^2 = 0
So [CH3]^2 = K1[CH3CHS] / 2K4
[CH3] = (K1[CH3CHS] / 2K4)^1/2 ...............(4)
Rate of reaction = d[C2H6] / dt = K4[CH3]^2 (Put 4 in this)
Rate of reaction = d[C2H6] / dt = K4 K1 [CH3CHS] / 2
K1K4 / 2 = K
Rate of reaction = K [CH3CHS]