Treatment of ammonia with excess of ethyl chloride will yield

The reaction showing the treatment of ammonia with excess ethyl chloride is given below:

Ammonia acts as a nucleophile and it attacks the electrophilic carbon of alkyl halide. 

It displaces the leaving group Cl⁻ and creates a new C−N bond. 

Excess ethyl chloride deprotonates the nitrogen center forming the secondary amine and thus the reaction goes on to form a mixture of primary amines, secondary amines, tertiary amines and quaternary ammonium salts (tetra-ethyl ammonium chloride).