Question

6. Use the bond energies listed in data sheet on the inside back cover of the lecture book to determine the energy of the reaction equation below, which represents the decomposition of hydrogen peroxide: 2HOOH(aq) 2H2O(l) + O2(g)

Answer 1

Answer :

The decomposition of hydrogen peroxide into water and oxygen is given as :

2H₂O₂ (l) $\rightarrow$ 2H₂O(l) + O₂(g)

From, the above equation it is clear that 2 moles of H₂O₂(l) forms 2 moles of water and one mole of oxygen after decomposition.

We can calculate the energy change of this reaction by considering the energy of the each individual bonds in the reactants and products.

The energy change of the reaction = Total bond energy of the reactant - Total bond energy of the products.

The bond energies are :

Bond	Energy (kj/mol)
O-H	463
O-O	146
O=O	498

There are 2 O-H bonds and one O-O bond present in the H₂O₂ .

Thus, the bond energy of H₂O₂ is = 2*463 + 146 = 1,072 kJ/mole

Hence, for 2 moles of H₂O₂ the total amount of bond energy is = 2 moles*1072 kJ/mole = 2,144 kJ

Thus, the bond energy of the reactants is = 2144 kJ

There are 2 O-H bonds present in the water.

Thus, the bond energy of water is = 2*463 = 926 kJ/mol

Thus, for 2 moles of water the amount of bond energy is = 2 moles*926 kJ/mole = 1,852 kJ

There is only one O=O bond present in the oxygen.

Thus, the bond energy of oxygen is = 498 kJ

Thus, the total bond energy in the products is = 1852 kJ + 498 kJ = 2,350 kJ

Hence, the change of the energy of the reaction is = total bond energy of reactants - total bond energy of the products = 2144 kJ - 2350 kJ = - 206 kJ.

Thus, the reaction is an exothermic reaction.

The change of the energy of the reaction is ∆H = -206 kJ