A gas stove burns propane (C₃H₈) to heat a house. The reaction is: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O + heat energy Where does the heat energy come from?

Question

A. The formation of bonds in carbon dioxide and water.
B. The breaking of the bonds in propane and oxygen.
C. The breaking of the bonds in carbon dioxide and water.
D. The formation of bonds in propane and oxygen.

Answer 1

The heat energy released in the combustion of propane comes from the formation of new bonds in the products (carbon dioxide and water) being stronger than the bonds that were broken in the reactants (propane and oxygen).

Thus, the correct answer is:

A. The formation of bonds in carbon dioxide and water.

When the bonds in the reactants break, energy is required (endothermic process), but when new bonds form in the products, energy is released (exothermic process), resulting in the surplus heat energy.