The reaction of CO, with an oxygen precovered Ag(110) surface leading to the formation of carbonate has been studied by scanning tunneling microscopy (STM) for different oxygen precoverages. For coverages below 0.5 monolayers (ML), the reaction is initiated preferentially at steps and defects and spreads uniaxially along the [001] directed, added -Ag-O- rows; For initial oxygen coverages below 0.25 ML, complete transformation to the carbonate structure is observed. For higher initial oxygen coverage, the unreacted rows are compressed to a (2X1) structure. In all cases, the ratio of carbonate ions formed to oxygen atoms consumed from added rows is close to 1:2. The reaction leads to a new reconstruction of the surface in which the carbonate ions are seen to reside preferentially on top of [1(1) over bar0$] directed triplet structures.