What characterizes an endothermic reaction?

An endothermic reaction is characterized by the absorption of heat from the surroundings. This means that during the reaction, energy in the form of heat is taken in, resulting in a temperature decrease in the surrounding environment. This is in contrast to exothermic reactions, which release heat, increasing the temperature of the surroundings.

In an endothermic process, the reactants have lower energy compared to the products. The absorption of thermal energy is necessary to overcome the energy barrier for the reaction to occur and to convert the reactants into higher-energy products. Common examples of endothermic reactions include photosynthesis and the dissolution of certain salts in water.

The option regarding constant temperature is more relevant to phase changes, like melting or boiling, rather than defining whether a reaction is endothermic or exothermic. While a catalyst can influence reaction rates, it does not determine whether a reaction is endothermic or exothermic; rather, it serves to lower the activation energy required for the reaction to proceed.