Question

use the mean bond enthalpies given below (in kj/mol) to calculate the enthalpy change of each reaction.
N2(g)+ 3H2(g) ---> 2NH3(g)
H2(g) + I2(g) ----> 2HI(g)
H2(g) + 1/2O2(g) ----> H2O(g)

N=N 944, H-H 436, N-H 388, I-I 151, H-I 299, O-H 463 and O=O 496.

AND CAN I BE EXPLAINED IT IN A WAY THAT IS SIMPLE PLEASE