Final answer:
The heat released when hydrogen burns in air to form water is due to the formation of hydrogen-oxygen bonds. Breaking the original hydrogen and oxygen bonds requires energy, but the formation of water molecules releases more energy, making the reaction exothermic. The correct answer is c) Forming hydrogen-oxygen bonds gives off energy.
Step-by-step explanation:
When hydrogen burns in air according to the equation 2H₂ + O₂ ⇒ 2H₂O, heat is released due to the exothermic nature of the chemical reaction. During this combustion reaction, energy is required to break the molecular bonds within the reactants.
Specifically, breaking the H-H bond in hydrogen and the O=O bond in oxygen are both endothermic processes, meaning they consume energy. However, the formation of O-H bonds in water molecules is an exothermic process, which releases energy.
The correct answer to the question is c) Forming hydrogen-oxygen bonds gives off energy. This is because, in the context of a chemical reaction, forming new bonds in the products (water in this case) results in a net release of energy.
The breaking of the original H-H and O=O bonds also requires energy, but this energy is less than what is released when the new O-H bonds are formed, resulting in an overall exothermic reaction where heat is given off.
Ultimately, breaking bonds (options a and b) absorbs energy and does not result in the net release of energy. Thus, the answer that forming the new bonds (option c) is responsible for the heat given off, is the correct one.
The heat comes from the new bonds in the products being stronger, and thus releasing more energy when formed, than the energy required to break the bonds in the reactants.