In presence of Lewis acid catalysts (anhydrous AlCl3 is a good example), Alkyl halides react with benzene to form alkyl benzenes.
C6H6 + CH3CH2Cl → C6H5CH2CH3 + HCl
The reaction is called Friedel-Crafts alkylation and it serves as a convenient way of inserting alkyl groups in the benzene ring, thereby opening the possibilities of further functionalization of the ring. The reaction operates through electrophilic aromatic substitution pathway.
However, after one ethyl group has been inserted, the reactivity of benzene ring towards incoming electrophile is enhanced and successive alkyl groups tend to enter into the benzene ring givng rise to a mixture of mono-, di- and tri- alkylated benzenes as the products.
Therefore Ethylbenzene will be one of the products for the given reaction.