What is true about exothermic reactions in thermodynamics?

In thermodynamics, exothermic reactions are defined by their ability to release energy into the surroundings, typically in the form of heat. This process results in an increase in the temperature of the surroundings as the reaction proceeds. This energy release is a key characteristic of exothermic reactions, making option B the correct answer.

When a chemical reaction occurs and energy is released, it indicates that the products of the reaction have lower energy than the reactants. This difference in energy is what drives the release of heat to the surroundings, and it is this property that distinguishes exothermic reactions from other types, such as endothermic reactions, which absorb energy.

In contrast, the other options describe characteristics that do not align with the fundamental nature of exothermic processes. For instance, the notion of absorbing energy is more aligned with endothermic reactions, while activation energy pertains to the energy required to initiate a reaction rather than indicative of the type of reaction that occurs. Lastly, stating that exothermic reactions do not change the temperature of the surroundings fails to recognize the essential energy transfer that occurs, which is a primary factor in these reactions.