Oxidising agent

An oxidising agent can convert an alcohol into a carboxylic acid with the same number of carbon atoms: ethanol becomes ethanoic acid, for example. This is different from burning the alcohol, which produces carbon dioxide and water.

An oxidising agent causes another substance to be oxidised. Here CuO supplies oxygen to H₂, so CuO is the oxidising agent. As it gives up oxygen, CuO is itself reduced.

Oxygen is an oxidising agent and supports combustion. The hot, glowing wood is already reacting slowly; a high concentration of oxygen allows the reaction to become vigorous enough for a flame to return. Oxygen supports the wood burning—it is not itself the fuel.