When hydrogen gas (H_2) reacts explosively with oxygen gas (O_2) to form water, where does the released energy originate?

• A. From the conversion of hydrogen atoms into helium
• B. From the formation of new bonds in H_2O, which releases energy
• C. From the breaking of H_2 and O_2 bonds, which releases energy
• D. From the absorption of energy from the surroundings

Answer: (B)

Verified step by step guidance

1. Understand that chemical reactions involve breaking old bonds and forming new bonds. Energy changes during a reaction depend on these processes.
2. Recognize that breaking bonds requires energy input (endothermic process), while forming bonds releases energy (exothermic process).
3. In the reaction of hydrogen gas (H_2) with oxygen gas (O_2) to form water (H_2O), bonds in H_2 and O_2 molecules are broken first, which consumes energy.
4. Next, new bonds are formed in the water molecules (O-H bonds), and this bond formation releases energy.
5. The net energy released in the reaction comes from the fact that the energy released by forming the new O-H bonds in water is greater than the energy required to break the original H-H and O=O bonds.