To find the molar enthalpy change follow these steps:
1) find the amount of heat released in this experiment, that is Q=mcT, where m is the mass or volume of solution used, T is the rise/drop in temperature and C is the specific heat capacity of water which is 4.18
Q= 500 × 4.18 ×(70-11)
= 123310 J
2) divide this value by 1000 to convert it into kJ
123310÷1000=
123.31
3) divide the value of energy released by number of moles , that is, mass/Mr
number of moles of Nitrogen = 20 ÷(14+14)
= 5/7 moles
molar enthalpy change= 123.31÷5/7
= 172.634 mol/kJ
