Is an endothermic reaction characterized as having a positive or negative delta H?

An endothermic reaction is characterized by a positive delta H (ΔH). This reflects that the reaction absorbs heat from its surroundings, leading to an increase in enthalpy. In thermodynamic terms, delta H represents the difference in energy between the reactants and products during a chemical reaction. For endothermic reactions, the energy of the products is greater than that of the reactants due to the absorption of heat, resulting in a positive value for delta H.

This positive delta H indicates that energy is required for the reaction to proceed, which is why heat must be supplied from the environment. Common examples of endothermic processes include photosynthesis and the melting of ice, both of which require energy input to occur.

In contrast, exothermic reactions release energy, leading to a negative delta H. Therefore, the distinction between positive and negative delta H is crucial for understanding the nature of the energy changes occurring during chemical reactions.