Final answer:
An exothermic reaction releases energy, for instance in the combustion of methane, while an endothermic reaction requires energy, such as in photosynthesis. The correct answer is A) Exothermic, Endothermic. Both types of reactions need an initial input of energy called the activation energy.
Step-by-step explanation:
An exothermic reaction releases energy/heat, whereas an endothermic reaction requires energy/heat. Therefore, the correct answer is A) Exothermic, Endothermic.
Exothermic reactions can be thought of as having energy as a product because they release energy to the surroundings. For example, the combustion of methane is exothermic as it releases heat. On the other hand, endothermic reactions absorb energy from the surroundings, thus having energy as a reactant. Photosynthesis is an example of an endothermic reaction because it requires sunlight to convert carbon dioxide and water into glucose.
All chemical reactions involve an activation energy, which is a small amount of energy required to initiate the reaction. Similarly, both endergonic and exergonic reactions need this initial energy to overcome the activation barrier.