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Endothermic processes refer to chemical reactions or physical changes that absorb heat from their surroundings. In these processes, the system (the substance undergoing the change) gains energy in the form of heat, typically resulting in a decrease in temperature of the immediate environment. The term "endothermic" originates from the Greek words *endo-* (meaning "within") and *-thermic* (related to heat), indicating that heat is absorbed into the system.

A classic example of an endothermic reaction is the dissolution of ammonium nitrate in water, which causes the solution to cool down. Similarly, photosynthesis is an endothermic process, as plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen. Another common example is the melting of ice, where thermal energy is absorbed to transition from a solid to a liquid state without raising the temperature further until the phase change is complete.

Endothermic reactions are often contrasted with exothermic reactions, which release heat into the surroundings. The distinction between the two is fundamental in thermodynamics, particularly in the study of enthalpy changes (ΔH). In an endothermic reaction, the enthalpy change is positive (ΔH > 0), indicating that the system has absorbed energy. This contrasts with exothermic reactions, where ΔH is negative (ΔH < 0), signifying heat release.

Endothermic processes are essential in various applications, including cooling systems, certain types of food preservation, and industrial manufacturing. For instance, some self-cooling beverage packs rely on endothermic reactions to maintain lower temperatures. Additionally, endothermic reactions play a role in biological systems, such as muscle contraction, where energy is absorbed to drive mechanical work. Understanding these processes is crucial for fields like chemistry, biology, and engineering, where energy transfer and efficiency are key considerations.