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. Cannot be determined
• C. Exothermic
• D. Endothermic

Answer: (C)

Verified step by step guidance

1. Identify the type of reaction given: 2H_2(g) + O_2(g) \rightarrow 2H_2O(l) is a combustion reaction where hydrogen gas reacts with oxygen gas to form liquid water.
2. Recall that combustion reactions typically release energy because new bonds formed in the products are stronger and more stable than the bonds broken in the reactants.
3. Understand that the formation of water from hydrogen and oxygen involves the creation of strong O-H bonds, which releases energy in the form of heat.
4. Use the concept of enthalpy change (\Delta H): if \Delta H is negative, the reaction is exothermic (releases heat); if positive, it is endothermic (absorbs heat).
5. Since the reaction forms stable water molecules and releases heat, conclude that the reaction is exothermic.