Compound formed when excess of ammonia gas reacts with chlorine is ammonium chloride.Explanation : $8 \mathrm{NH}_3 \; \text{ (excess) } \; +3 \mathrm{Cl}_2 \rightarrow \mathrm{N}_2 +6 \mathrm{NH}_4 \mathrm{Cl}$Yellowish green colour of chlorine disappears and white fumes of ammonium chloride are formed.