Question

Calculate the enthalpy change for the reaction below using the given bond dissociation energies:2HBr (g) + Cl2 (g) -> 2HCl (g) + Br2 (g)Bond dissociation energies:H-H = 436 kJ/molBr-Br = 193 kJ/molH-Br = 366 kJ/molCl-Cl = 242 kJ/molH-Cl = 431 kJ/mol

Answer 1

To calculate the enthalpy change for the reaction, we can use the bond dissociation energies given. The enthalpy change for the reaction can be found using the following equation:H =   bond dissociation energies of bonds broken  -   bond dissociation energies of bonds formed In this reaction, the bonds broken are:- 2 H-Br bonds in 2HBr- 1 Cl-Cl bond in Cl2The bonds formed are:- 2 H-Cl bonds in 2HCl- 1 Br-Br bond in Br2Now, we can plug in the bond dissociation energies into the equation:H = [ 2  366 kJ/mol  +  1  242 kJ/mol ] - [ 2  431 kJ/mol  +  1  193 kJ/mol ]H = [ 732 kJ/mol  +  242 kJ/mol ] - [ 862 kJ/mol  +  193 kJ/mol ]H =  974 kJ/mol  -  1055 kJ/mol H = -81 kJ/molThe enthalpy change for the reaction is -81 kJ/mol.