We present a chemical reaction network that describes the condensation chemistry of carbon dust grains in an expanding supernova shell. We assume that the region of interest consists solely of gaseous free carbon and oxygen atoms and that the buildup of CO is counteracted by the radioactive decay of ~(56)Co, which breaks up the CO molecule and allows C to condense into solids. Our chemical model takes C to first form linear chains, which, at some critical length, transition into ringed isomers. These isomers are more resistant to oxidation than linear chains. These ringed isomers form the nuclei for the growth of larger carbon solids. The effect of the disruption of CO on grain growth is displayed, leading to a rethinking of previous assumptions on the importance of CO disruption. How the abundance and size distribution of grains are affected by various parameters of the ejecta is also studied, providing insight into the possible sites of grain condensation.
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