Final answer:
The reaction in question is exothermic, as combustion reactions like this one typically release heat, leading to a negative enthalpy change.
Step-by-step explanation:
The question refers to the reaction 2CH₃OH (l) + 3O₂ (g) → 2CO₂ (g) + 4H₂O (g) which depicts the combustion of methanol. To classify this reaction as either exothermic or endothermic, we need to consider the enthalpy change associated with it. While the specific energy change for the given mass (20.8 g of methanol) is not provided, combustion reactions are generally exothermic because they release heat. Therefore, the correct answer is (a) Exothermic.
In the context of the SEO keywords provided, it's helpful to understand that in an exothermic reaction, energy is released to the surroundings, typically as heat, resulting in a negative enthalpy change (ΔH). Conversely, in an endothermic reaction, energy is absorbed from the surroundings, leading to a positive enthalpy change. This concept ties back to the fact that combustion reactions are typically exothermic because they involve the release of energy to the environment.