Question

When propane burns in air (C₃H₈ + 5O₂ → 3CO₂ + 4H₂O), the reactant bonds must first be broken before product bonds can form. Which process requires an input of energy?

(1 point)
Responses

The collision of reactant molecules before reacting.
The collision of reactant molecules before reacting.

Breaking the bonds in propane and oxygen molecules.
Breaking the bonds in propane and oxygen molecules.

Both breaking reactant and forming product bonds.
Both breaking reactant and forming product bonds.

Forming the bonds in carbon dioxide and water.

Answer 1

Breaking the bonds in propane and oxygen molecules.

Explanation: bond breaking is endothermic (requires energy input) while bond formation releases energy; in combustion the energy required to break C–H, C–C and O=O bonds is supplied, and more energy is released when CO₂ and H₂O bonds form.