The chemical equation for the reaction between ethyl iodide and aqueous potassium hydroxide (KOH) is:

C2H5I + KOH -> C2H5OH + KI

In this reaction, ethyl iodide (C2H5I) reacts with potassium hydroxide (KOH) to form ethanol (C2H5OH) and potassium iodide (KI). The reaction is an example of a nucleophilic substitution reaction, where the hydroxide ion (OH-) from KOH acts as a nucleophile and attacks the carbon atom of the ethyl iodide, displacing the iodide ion (I-).