Which of the following chemical equations represents an endothermic reaction?

• A. NaOH(s) + H_2O(l) ightarrow Na^+(aq) + OH^-(aq) + heat
• B. N_2(g) + 3H_2(g) ightarrow 2NH_3(g) + heat
• C. CH_4(g) + 2O_2(g) ightarrow CO_2(g) + 2H_2O(g) + energy
• D. 2H_2O(l) + energy ightarrow 2H_2(g) + O_2(g)

Answer: (D)

Verified step by step guidance

1. Understand the difference between endothermic and exothermic reactions: endothermic reactions absorb energy (heat) from the surroundings, while exothermic reactions release energy (heat) to the surroundings.
2. Look at the chemical equations and identify where heat or energy appears in the reaction. If heat or energy is written on the reactant side, the reaction is endothermic because it requires energy input.
3. If heat or energy is written on the product side, the reaction is exothermic because it releases energy during the reaction.
4. Analyze each given equation: - For example, in the equation \(\mathrm{NaOH(s) + H_2O(l) \rightarrow Na^+(aq) + OH^-(aq) + heat}\), heat is produced, so it is exothermic. - In the equation \(\mathrm{2H_2O(l) + energy \rightarrow 2H_2(g) + O_2(g)}\), energy is consumed, indicating an endothermic reaction.
5. Conclude that the equation with energy or heat on the reactant side represents the endothermic reaction.