Question

If the bonds in the reactants of Figure 7-3 contained 432 kJ of chemical energy and the bonds in the
products contained 478 kJ of chemical energy, what would be the amount of energy change during the
reaction? Would this energy be absorbed or released? Show your work.

Answer 1

Answer:

• The energy change would be 46kJ

• The energy would be absorbed

Explanation:

The energy change during a chemical reation, i.e. the reaction energy, is equal to the chemical energy stored in the bonds of the products less the chemical energy stored in the bonds of the reactants.

Hence:

• Energy change = 478 kJ - 432kJ = 46kJ

The change is positive, this is, the chemical energy of the products is greater than the chemical energy of the reactants.

That corresponds to the second graph, where the level of the energy of the products in the graph is higher than the level of the energy of the reactants. Therefore, the conclusion is that the reaction absorbed energy and it is endothermic.