How do you calculate lattice energy?

Energy change of chemical reaction?

• Calculate the energy change in kJ for the formation of 1.19 mol of KBr(s) given the following information: Br2(l) → Br2(g) : 30.92 KJ/mol K(g) → K(s) : −180.4 KJ/mol 1/2 Br2(g) → Br(g) : 127.33 KJ/mol K(g) → K+(g) + e− : 419 KJ/mol Br− → Br(g) + e− : 324.7 KJ/mol Lattice energy for KBr = −689 KJ/mol

• Answer:

  To form KBr, the total reaction scheme is: 1/2 Br2(l) + K(g) → K(s) + Br(g) K(g) + Br(g) → K+(g) + Br−(g) K+(g) + Br−(g) → KBr(s) So, the energy for those is 1/2 (30.92 kJ/mol) + −180.4 kJ/mol 419 kJ/mol - 324.7 kJ/mol and −689 kJ/mol The total is -759.64 kJ/mol You have 1.19 mol of KBr, so the energy change is -903.97 kJ, or -904 (with significant figures)