Final answer:
Side products in chemical reactions, like the CO formed during methane combustion, are often not seen because they can react further or be removed. The theoretical yield assumes complete conversion to the main product, but side reactions and incomplete reactions can affect the actual yield.
Step-by-step explanation:
In chemical reactions, side products may form along with the desired products. In the combustion of methane, for example, carbon monoxide (CO) can be a side product alongside the main product, carbon dioxide (CO2). We do not typically see this side product because it might react further or be removed as it is formed. For instance, CO can further oxidize to CO2 in the presence of excess oxygen. When calculating the theoretical yield, we assume all reactants convert to the desired products, ignoring side products and incomplete reactions. This theoretical yield is determined using the balanced chemical equation but may differ from the actual yield due to side reactions and incomplete conversion.