Determine if the bond between each pairs of atoms would be pure covalent, polar covalent, or ionic. n and se

Types of Bonds can be predicted by calculating the difference in electronegativity.

If, Electronegativity difference is,

                Less than 0.4 then it is Non Polar Covalent Bond

                Between 0.4 and 1.7 then it is Polar Covalent Bond

                Greater than 1.7 then it is Ionic

For N and Se,

                    E.N of Nitrogen         =   3.04

                    E.N of Selenium        =   2.55

                    E.N Difference             0.49          (Weakly Polar Covalent)

As you have not provided remaining pairs, so if you have any of them, follow the method as mentioned above.

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.