Question

The compound calcium cyanamide (CaNCN) is used as a nitrogen source for crops. To obtain this compound, calcium carbide is reacted with nitrogen at high temperatures. CaC2(s) + N2(g) CaNCN(s) + C(s) What mass of CaNCN can be produced if 7.45 mol CaC2 reacts with 5.85 mol N2?

Answer 1

N2 + CaC2 = CaNCN + C 
As you can see, 1 mol of N2 can react completely with 1 mol of CaC2 and 1 mol of CaNCN will be obtained 
It means 5 mol of N2 can react completely with 5 mol of CaC2 and 5 mol of CaNCN will be obtained 

So, there are 7.5 - 5 = 2.5 odd mole of CaC2 after the reaction 
And the mass of obtained CaNCN is 
m = n*M = 5*80 = 400g