Several processes are given in the table and labeled as endo- thermic or exothermic and given a sign for ∆H°. Which process is labeled with the correct sign of ∆H° and correct classification as endothermic or exothermic? (LO 9.8) Process (c) Water freezes into ice in the freezer.

Key Concepts

Enthalpy Change (∆H°)

Enthalpy change, denoted as ∆H°, is a measure of the heat content of a system at constant pressure. It indicates whether a process absorbs heat (endothermic, ∆H° > 0) or releases heat (exothermic, ∆H° < 0). Understanding this concept is crucial for classifying chemical and physical processes based on their thermal energy changes.

Endothermic and Exothermic Processes

Endothermic processes absorb heat from their surroundings, resulting in a positive enthalpy change (∆H° > 0), while exothermic processes release heat, leading to a negative enthalpy change (∆H° < 0). Recognizing these classifications helps predict the thermal behavior of reactions and physical changes, such as melting and freezing.

Phase Changes

Phase changes, such as freezing and melting, involve transitions between solid, liquid, and gas states. The freezing of water into ice is an exothermic process because it releases heat to the surroundings, resulting in a negative ∆H°. Understanding phase changes is essential for correctly identifying the thermal nature of processes involving state transitions.