Question

Calculate the bond dissociation energy of the nitrogen-nitrogen (N-N) bond in N2O4 given that the enthalpy change for the reaction 2N2O4(g) --> 4NO2(g) is -109.7 kJ/mol.

Answer 1

To calculate the bond dissociation energy of the N-N bond in N2O4, we need to consider the enthalpy change for the given reaction and the bond dissociation energy of the N-O bond in NO2.The given reaction is:2N2O4 g  --> 4NO2 g   H = -109.7 kJ/molFirst, we need to find the bond dissociation energy of the N-O bond in NO2. The enthalpy change for the dissociation of one mole of NO2 is given by the following reaction:NO2 g  --> NO g  + 0.5O2 g   H = +33.18 kJ/molNow, let's consider the dissociation of one mole of N2O4 into NO2 and N2:N2O4 g  --> N2 g  + 2NO2 g To find the enthalpy change for this reaction, we can use the enthalpy change for the given reaction and the enthalpy change for the dissociation of one mole of NO2:H N2O4  = 0.5 * H 2N2O4  - 2 * H NO2 H N2O4  = 0.5 *  -109.7 kJ/mol  - 2 *  +33.18 kJ/mol H N2O4  = -54.85 kJ/mol - 66.36 kJ/molH N2O4  = -121.21 kJ/molThe bond dissociation energy of the N-N bond in N2O4 is equal to the enthalpy change for the dissociation of one mole of N2O4:Bond dissociation energy  N-N  = -H N2O4  = 121.21 kJ/mol