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Enthalpy is the transfer of energy in a reaction (for chemical reactions, it is in the form of heat) and is the change in enthalpy. Δ H {\displaystyle \Delta H} is a state function, meaning that Δ H {\displaystyle \Delta H} is independent of processes occurring between initial and final states.
The Mollier enthalpy–entropy diagram for water and steam. The "dryness fraction", x , gives the fraction by mass of gaseous water in the wet region, the remainder being droplets of liquid. An enthalpy–entropy chart , also known as the H – S chart or Mollier diagram , plots the total heat against entropy, [ 1 ] describing the enthalpy of a ...
The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".
Enthalpy (/ ˈ ɛ n θ əl p i / ⓘ) is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. [1] It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant external pressure, which is conveniently provided by the large ambient atmosphere.
Temperature-dependency of the heats of vaporization for water, methanol, benzene, and acetone. In thermodynamics, the enthalpy of vaporization (symbol ∆H vap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy that must be added to a liquid substance to transform a quantity of that substance into a gas.
The enthalpy of solution is most often expressed in kJ/mol at constant temperature. The energy change can be regarded as being made up of three parts: the endothermic breaking of bonds within the solute and within the solvent, and the formation of attractions between the solute and the solvent. An ideal solution has a null enthalpy of mixing.
Enthalpies of melting and boiling for pure elements versus temperatures of transition, demonstrating Trouton's rule. In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid, at constant pressure.
For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. The enthalpy of reaction can then be analyzed by applying Hess' law, which states that the sum of the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction.