Can a reaction be both exothermic and endothermic?

No, a reaction cannot be both exothermic and endothermic at the same time.

In chemistry, a reaction is classified as either exothermic or endothermic based on the energy changes that occur during the reaction. An exothermic reaction is one in which energy is released, usually in the form of heat. This means that the energy of the products is less than the energy of the reactants. The excess energy is released to the surroundings, causing an increase in temperature. Examples of exothermic reactions include combustion reactions and many oxidation reactions.

On the other hand, an endothermic reaction is one in which energy is absorbed from the surroundings, usually also in the form of heat. This means that the energy of the products is greater than the energy of the reactants. The absorbed energy is used to break the bonds in the reactants, causing a decrease in temperature. Examples of endothermic reactions include photosynthesis and the process of evaporation.

Therefore, a reaction cannot be both exothermic and endothermic at the same time because these terms describe opposite energy changes. A reaction can either release energy (exothermic) or absorb energy (endothermic), but it cannot do both simultaneously.

However, it's important to note that in a series of chemical reactions, some individual reactions may be exothermic while others may be endothermic. For example, in a biochemical pathway in a living organism, some steps may release energy while others may require energy. But each individual reaction within the pathway is still classified as either exothermic or endothermic, not both.