Given the reaction: 2H_2(g) + O_2(g) ightarrow 2H_2O(l), predict whether this reaction is exothermic or endothermic.

• A. Neither exothermic nor endothermic
• B. Exothermic
• C. Endothermic
• D. Cannot be determined

Answer: (B)

Verified step by step guidance

1. Understand the definitions: An exothermic reaction releases heat to the surroundings, while an endothermic reaction absorbs heat from the surroundings.
2. Look at the reaction given: \$2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$. This is the formation of liquid water from hydrogen and oxygen gases.
3. Recall that forming water from hydrogen and oxygen is a combustion-like process, which is known to release energy in the form of heat and light.
4. Consider bond energies: Breaking the \(H-H\) and \(O=O\) bonds requires energy (endothermic step), but forming the \(O-H\) bonds in water releases more energy (exothermic step). The net effect is a release of energy.
5. Therefore, since the overall reaction releases heat, it is classified as an exothermic reaction.