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Nikita Parmar

Updated on 12th July, 2023 , 6 min read

Enthalpy of Atomisation: Definitions, Examples, Reactions, Calculation of Enthalpy, and Change of Atomisation

Enthalpy of Atomisation Overview

New goods are created by every spontaneous process. Some of the processes that we are aware of take energy, while others cause energy to evolve. Consequently, we constantly see a change in enthalpy as a result of processes being completed. This enthalpy shift may be the result of atomization, solution, etc. It is possible to define enthalpy as the change in enthalpy that is predominantly brought on by the dissolution of one mole of bonds to create atoms in the gas phase. Because internal energy was designed primarily for volatile processes, the thermodynamic notion of enthalpy was created to study reactions under constant pressure. 

What is Atomisation?

An analyte in solid, liquid, or solution form is transformed into a free gaseous atom by the process of atomization. It is the process by which a liquid in bulk is converted into a spray of liquid droplets in a gas or vacuum. All metals that can be industrially melted are included in the list of metals that can be atomized.

Enthalpy of Atomisation

What is the Enthalpy of Atomisation?

The energy produced when a mole of atoms is created from an element in its gaseous state is known as the enthalpy of atomization (H). The amount of energy needed to dissolve the chemical bonds holding the molecules' atoms together is measured by the enthalpy of atomization. Numerous elements have high atomicities, which means that it requires a lot of energy to break the chemical bonds that hold the atoms together. This is due to the atoms' strong covalent bonds holding them together. Since hydrogen has a low enthalpy of atomization, the atomic bonds between its atoms may be broken with relatively little energy. This is due to the weak hydrogen bonds that hold hydrogen atoms together.

Example of Atomisation

Atomization of the methane molecule.

Enthalpy of Atomisation

Definition of Enthalpy of Atomisation

Understanding the number "Enthalpy" H and how it came to be is necessary before we can grasp the enthalpy of atomization. 'Atomization' is the process of breaking down into atoms. In the laboratory, chemical reactions take place under atmospheric pressure, which is a constant. Enthalpy was created to evaluate constant pressure processes since internal energy U, was established primarily for constant volume reactions. Every natural activity produces new things. While some well-known human activities drain energy, others lead to the development of energy.  As a result, when an activity is finished, there is always a change in enthalpy. Atomization enthalpy, solution enthalpy, or other variables may be responsible for this enthalpy change. Different chemical processes, such as combustion, atomization, hydration, solution, neutralization, and phase transitions, such as vaporization and fusion, may result in the shift of heat.

Enthalpy of Atomisation

Enthalpy of Atomisation: Reactions

When one mole of bonds is completely broken to produce atoms in the gas phase, the enthalpy changes. This change is called the enthalpy of atomization (aH0). Take the atomization of a methane molecule as an illustration. For diatomic compounds, the enthalpy of bond dissociation equals the enthalpy of atomization. 

How Enthalpy of Atomization is Calculated?

Enthalpy change equals the change in a system's internal energy if pressure is kept constant. The enthalpy of atomization is therefore equal to the product of the enthalpies of fusion and vaporization. For instance, the bond energy of the diatomic molecule chlorine gas (Cl2) is all that is needed to determine the enthalpy of atomization under normal circumstances. The chemical may be atomized by simply rupturing the bonds that hold gaseous molecules together. Atomization of sodium (Na) metal under ordinary circumstances entails dissolving atoms connected by metallic bonds. The enthalpy of fusion and the enthalpy of sodium vaporization are added to get the enthalpy of atomization. The enthalpy of atomization and sublimation is the same for every elemental solid.

Read more about the Enthalpy Formula and Frenkel Defects.

Enthalpy of Atomization of Transition Elements

  1. It is well known that D-block elements have higher melting and boiling points
  2. A higher melting point element has greater metallic bonding energy. 
  3. The energy of metallic bonding is determined by the atomization enthalpy. 
  4. Atomization energy increases in direct proportion to the number of unpaired electrons in the d-orbital. 
  5. As the number of unpaired electrons rises, the enthalpy of atomisation of transition elements also rises. 
  6. Interatomic interactions increase in proportion to the number of unpaired electrons. 
  7. When electron pairing takes place, melting temperatures in the second part of the transition series decrease. 
  8. Unpaired electrons are observed to rise as they go from left to right in a period.
  9. Cobalt, for instance, has a melting point of 1768 K, but iron has a melting temperature of 1808 K. Because there are more electrons in iron's d-orbitals than in copper's, iron has a greater enthalpy of atomisation than copper. 
  10. The electrical configuration of cobalt is 3d74s2, whereas that of iron is 3d64s2. There are three unpaired electrons in all. Iron has a higher enthalpy of atomisation due to the greater number of unpaired electrons in the metal.

Points to remember

  1. When a mole of a material in the gaseous state is divided into its individual atoms, the enthalpy of atomisation changes.
  2. The enthalpy of a solution at a constant temperature is often expressed as kJ/mol.
  3. The lattice enthalpy of an ionic compound is the enthalpy change that takes place when one mole of an ionic compound dissociates into ions.
  4. The energy produced when a molecular chain of bonds is created from lone atoms in a gaseous state is known as bond enthalpy.
  5. The change in enthalpy that takes place when a substance dissolves in a solvent under constant pressure, resulting in infinite dilution, is known as the enthalpy of the solution, also known as the enthalpy of dissolution or heat of solution.
  6. The heat exchange when one mole of material is entirely burned or oxidized by oxygen is known as the enthalpy of combustion.

Sample Questions related to Enthaply of Atomisation

Sample Question 1: Which element has the highest atomisation enthalpy between Sc and Zn? How is atomisation energy determined?

Solution: The answers are Sc and Zn, which are elements in the PF group's third periodic table. The degree of metallic bonding affects an element's atomization enthalpy. The greater an element's atomisation enthalpy, the stronger it's metallic bonding. The enthalpy changes proportionally to changes in the system's internal energy, while the pressure stays constant. The enthalpies of fusion and vaporization, therefore, balance out to equal the enthalpy of atomization.

Sample Question 2: What causes the low atomisation enthalpy of alkali metals?

Solution: The enthalpies of atomisation are thought of as positive when the atoms need to be given energy in order to be separated. The atomic radii of a set of alkali metals increase from top to bottom due to the addition of additional electron shells. Alkali metals have a low atomisation enthalpy because it is simpler to separate bigger atoms with less energy input since larger atoms attract each other with less force than smaller atoms do.

Sample Question 3: Why do transition elements exhibit higher atomisation enthalpies? What is the source of the endothermic atomisation enthalpy?

Solution: Because they have d-orbitals, transition elements have higher enthalpies of atomisation. These d-orbitals contain unpaired electrons. Unpaired electrons enhance interatomic interactions, which reduce atomisation heat. More unpaired electrons in the d-block make transition enthalpies higher. The energy required to remove one electron from each mole of free gaseous atoms of that element is known as the initial ionization energy. Atomization and ionization enthalpies are still positive (endothermic).

Sample Question 4: What does "enthalpy of atomization" mean exactly? Are the atomization and bonding enthalpies the same?

Solution: The enthalpy shift that takes place when a complex's bonds break down and its component atoms are reduced to single atoms is known as the atomization enthalpy. The enthalpy transition that takes place when 1 mol of material completely dissociates into atoms under typical conditions (298.15 K, 1 bar) is known as the ordinary atomization enthalpy. The enthalpy change that takes place when one mole of gaseous atoms is created from atomic matter (atH) is known as the atomization enthalpy. On the other hand, the energy needed to dissolve one mole of a bond and create separate atoms in a gaseous state is known as bond enthalpy, bond energy, or bond dissociation enthalpy.

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Frequently Asked Questions

Is the enthalpy of atomisation the same as the enthalpy of bonds?

Ans. The change in enthalpy that occurs when one mole of gaseous atoms is created from an atomic substance is known as atomization enthalpy (atH). Bond enthalpy, bond energy, and bond dissociation enthalpy, on the other hand, are the energies required to dissociate one mole of a bond into separate atoms in the gaseous state.

Why is the enthalpy of atomization endothermic?

Ans. The initial ionization energy of an atom is the energy required to separate one electron from each mole of free gaseous atoms of that element. Atomization enthalpies and ionization enthalpies are still positive (i.e., endothermic).

How is atomisation energy determined?

Ans. The change in enthalpy is proportional to the change in a system’s internal energy if pressure is maintained constant. As a result, the fusion and vaporization enthalpies are added to determine the atomiation enthalpy.

Give an example of the enthalpy of atomisation.

Ans. Atomization of the methane molecule.

What does the term "enthalpy of atomisation" mean?

Ans. The amount of enthalpy modification that occurs as a complex’s bonds are broken and its constituent atoms are separated into individual atoms is known as atomisation enthalpy. Ordinary atomization enthalpy is the change in enthalpy as 1 mol of a substance entirely dissociates via atoms at standard temperatures (298.15 K, 1 bar).

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