.D. Chapple-Sokol, C.J. Giunta, and R.G. Gordon (J. Electrochem. Soc. 136, 2993

Question

.D. Chapple-Sokol, C.J. Giunta, and R.G. Gordon (J. Electrochem. Soc. 136, 2993 (1989)) proposed the following radical chain mechanism for the initial stages of the gas-phase oxidation of silane by nitrous oxide: a. N2O N2 + O b. O + SiH4 SiH3 + OH c. OH + SiH4 SiH3 + H2O d. SiH3 + N2O SiH3O + N2 e. SiH3O + SiH4 SiH3OH + SiH3 f. SiH3 + SiH3O (H3Si)2O Label each step with its role in the chain. Use the steady-state approximation to show that this mechanism predicts the following rate law for SiH4 consumption (provided ka and kf are in some sense small)

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Explanation / Answer

(1) N2O N2 + O.      k1

(2) O. + SiH4 SiH3. + HO. k2

(3) HO. + SiH4 SiH3. + H2O k3

(4) SiH3. + N2O SiH3O. + N2 k4

(5) SiH3O. + SiH4 SiH3OH + SiH3.    k5

(6) SiH3. + SiH3O. (H3Si)2O k6

vr = {(k1 k4 k5) / k6} 1/2 [N2O][SiH4]1/2

d[SiH4] /dt = -k[N2O][SiH4]1/2

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