Final answer:
The chemical reaction 2 H₂(g) + O₂(g) → 2 H₂O(g) is exothermic and generally spontaneous under normal conditions as it releases energy and results in increased entropy.
Step-by-step explanation:
The reaction 2 H₂(g) + O₂(g) → 2 H₂O(g) is an exothermic reaction. In an exothermic reaction, energy is released into the surroundings typically in the form of heat, as indicated by a positive amount of energy or heat being shown on the product side of the reaction equation. For instance, 2H₂(g) + O₂(g) → 2H₂O(l) + 135 kcal showcases that 135 kcal of heat is released when water is formed, which makes it exothermic.
On the other hand, an endothermic reaction absorbs energy from the surroundings, which is often indicated by a positive amount of energy or heat being on the reactant side of the equation, like in N₂(g) + O₂(g) + 45 kcal → 2NO(g), signifying that 45 kcal of energy is absorbed during the reaction.
Concerning spontaneity, a spontaneous reaction occurs without the constant input of energy and may be exothermic or endothermic, depending on other thermodynamic factors like entropy and free energy change (ΔG). The reaction in question is generally regarded as spontaneous under normal conditions because the formation of water from hydrogen and oxygen releases energy and results in an increase in entropy.