Standard enthalpy of Atomization

Chemical Thermodynamics: Standard enthalpy of Atomization

Atomization refers to the separation of bulk materials and breaking them up to fine particles. This transformation goes takes place up breaking up of liquid jet into a number of filaments, which in turn transform into droplets.Common home atomizers that you may be familiar with are shower heads, perfume sprays, garden hoses, deodorant and hair sprays.A spray is a cluster of moving droplets that usually move in a controlled fashion. Naturally occurring sprays include rain and ocean sprays.A droplet is a small particle of liquid in a spherical shape.In chemical thermodynamics, atomization means breaking molecules to form singular atoms in the gaseous phase. Types of atomizers either use pressure (Airless), air, centrifugal force, electrostatic energy or ultrasonic technology to undertake atomization.

Figure : Atomization of diatomic molecules.

Figure : Atomization of metal lattices

The atomization enthalpy , of an elementis the change in heat energy of the system when one mole of free gaseous atoms of an element is formed from the element itself in its standard state under standard conditions (1 atm, 298 K).Heats of atomization are always denoted with a positive sign, because they represent processes in which energy is absorbed to break bonds. In physical terms, this heat is related to the latent heat of vaporization.

Enthalpies of atomization can appear in different ways but the equation that describes the process remains true to the theory. Hence, enthalpies of atomization can also appear as bond dissociation enthalpies for diatomic molecules.Consider the following example of atomizing chlorine molecules, Cl2. Below are the equations describing the enthalpy of atomization of chlorine and the bond dissociation enthalpy of chlorine:

Notice that the bond dissociation enthalpy of chlorine is double its enthalpy of atomization. The enthalpy change of atomization of gaseous water is the sum of the HO–H and H–O bond dissociation enthalpies. Likewise, you may be supplied data describing either of the two processes, so make sure you know the definitions for the various enthalpy changes and their respective equations. For example, the enthalpy of atomization of metal might also be represented asthe enthalpy of sublimation. Herein, sublimation is the process where a solid convert directly into a gas without passing through the liquid state. Likewise, when a diatomic element is transformed to gaseous atoms, only half a mole of molecules areneeded. This is because the standard enthalpy change is based on the production of one mole of gaseous atoms. Therefore, when the atoms in the molecule are different isotopes of the same element the calculation becomes non-trivial.

In this case, it isthedenoted as the enthalpy of sublimation for copper solid, at 1 atm and 25C.

The atomisation enthalpy of a compound is the energy needed to convert 1 mole of a compound into its free gaseous atoms under standard states. Eg. CH4(g) –> C(g) + 4H(g). Likewise, atomization enthalpies can be utilized to analyse the enthalpy changes required to form free gaseous atoms.


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