Question

Nitrogen and hydrogen combine at high temperature, in the presence of a catalyst, to produce ammonia: Assume 0.220 mol of N2 and 0.721 mol of H2 are present initially. How many moles of H2 remain? N_2+3H_2--->2NH_3 I know that N_2 is the limiting reactant. 0.220 mol of N_2 will produce 0.440 on ammonia. how do i find the moles of hydrogen remaining?