Dannelsesentalpier

Dannelsesentalpier, often referred to as enthalpy of formation, is a fundamental thermodynamic concept used to quantify the heat change associated with the formation of one mole of a substance from its constituent elements in their standard states. This value is crucial in thermochemistry, allowing for the calculation of the enthalpy change of a wide variety of chemical reactions. The standard state of an element is typically defined as its most stable form at 298.15 Kelvin (25 degrees Celsius) and 1 atmosphere pressure. For example, the standard state of oxygen is O2 gas, and that of carbon is graphite.

By convention, the enthalpy of formation of elements in their standard states is defined as zero. This provides a reference point for measuring the energy stored or released when compounds are formed. For instance, the dannelsesentalpi of water (H2O) refers to the enthalpy change when one mole of liquid water is formed from one mole of hydrogen gas (H2) and half a mole of oxygen gas (O2). A negative dannelsesentalpi indicates an exothermic reaction, meaning energy is released during formation, while a positive value signifies an endothermic reaction, requiring energy input. These values are typically found in thermodynamic tables and are essential for predicting reaction spontaneity and energy requirements.