Compounds of silicon with hydrogen and alkyl groups

4 Compounds of silicon with hydrogen and alkyl groups 

Using values of AGf from the Data Book, calculate AG for the reaction of (a) methane, CH4, and (b) ethane, C2H6, with oxygen to give CO2 and H2O. Calculate AG, values for the analogous reactions of (c) monosilane, SiH4, and (d) disilane, Si2H6. 

The values you obtain from the calculations in Question 10.9 show you that, in oxygen, both alkanes are unstable with respect to CO2 and H2O, and both silanes are also unstable with respect to Si02 and H2O. The silanes are spontaneously flammable in air, but the alkanes are not. Methane (natural gas) can, of course, explode in air if it is sparked. 

The alkanes possess a kinetic stability to reaction with O2 that the silanes do not. The reasons for this must lie in the mechanism of the reactions, and are probably concerned with the larger size of the silicon atom, which facilitates nucleophilic attack by OH , and its ability to expand its octet. The explosive reaction of methane when sparked is due to the production of radical species, such as CH3, which initiate a chain reaction. 

An unbranched silicone chain (R is an alkyl group, usually methyl). 

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