Hi,

When acetic acid reacts with phosphorus pentoxide, acetic anhydride is obtained.

On heating Acetic acid with P2O5, it will form ethanoic anhydride . Acetic acid is the common name of ethanoic acid. The chemical formula of it is CH3-OOH. It is a carboxylic acid with two C atoms. P2O5 is phosphorus pentaoxide that is a very good dehydrating agent and involves in dehydration reactions of carboxylic acids mainly. Here when acetic acid is heated with P2O5, it will form ethanoic anhydride.

2Ch3-COOH + P2O5 = CH3-CO-O-CO-CH3 + H2O.

Hope this helps.

Good luck.