DeltaH

DeltaH, often denoted as ΔH, is a thermodynamic variable that represents the change in enthalpy of a system during a process. Enthalpy itself is a measure of the total heat content of a system, encompassing its internal energy and the product of its pressure and volume. The change in enthalpy, therefore, quantifies the heat absorbed or released by a system at constant pressure.

In chemical reactions, ΔH is a crucial indicator of whether a reaction is exothermic or endothermic. A negative ΔH signifies an exothermic reaction, where heat is released into the surroundings, causing the surroundings to warm up. Conversely, a positive ΔH indicates an endothermic reaction, which absorbs heat from the surroundings, leading to a decrease in the temperature of the surroundings.

The units of ΔH are typically joules (J) or kilojoules (kJ) per mole (mol) when referring to chemical reactions. This allows for the comparison of the energetic impact of different reactions. For instance, the enthalpy of formation, a specific type of ΔH, refers to the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states. Understanding ΔH is fundamental to comprehending energy transformations in physical and chemical processes, impacting fields from chemistry and physics to biology and engineering.