Question

The equation for the oxidation of H2 is 2H2+O2→2H2O

The total energy of the reactant side is 1,356 kJ/mol.
The total energy of the product side is 1,868 kJ/mol.
What is the total change in bond energy?
Is this reaction endothermic or exothermic?

Answer 1

The process may not be obvious at first, but it is straightforward, unlike many things in chemistry.

You can start with the change in bond energy simply by subtracting the reactants’ energies from the product’s energy.
1868 kJ/mol - 1356 kJ/mol = 512 kJ/mol.

To determine whether the reaction is endo or exothermic, simply look at the change in energy in the reaction. Since the product has more total energy than the reactants, the reaction is endothermic.