# Born-Haber Cycle: Formation of a Chlorine Atom

• henry3369
In summary, the conversation discusses the formation of an atom from a molecule in a Born-Haber cycle, using the example of a chlorine atom from a chlorine molecule. The question is raised about why the bond energy is halved in the reaction, and it is suggested that thinking in terms of moles may be more helpful.
henry3369

## Homework Statement

I don't actually need help with an entire problem, I just can't seem to figure out what goes on when an atom is formed from a molecule in a Born-Haber cycle.

For example:
The formation of a chlorine atom from a chlorine molecule
(1/2)Cl2 → Cl(g) ΔH = (1/2) x bond energy of Cl2 = +122 kJ

## The Attempt at a Solution

Why is the bond energy being halved? It you have a Cl2 molecule, and you need 244 kJ to break the bond into two Cl atoms. Why would the formation of a Cl atom be only half of that then?

Doesn't that (1/2) factor mean something?

Here, it might be more useful to think in terms of moles. Reacting one mole of Cl2 takes 244 kJ, and making one mole of chlorine atoms requires reacting 0.5 moles of Cl2.

## 1. How does the Born-Haber Cycle explain the formation of a chlorine atom?

The Born-Haber Cycle is a series of interconnected steps that explain the formation of a chlorine atom from its constituent elements, chlorine gas and sodium metal. It takes into account the various energy changes involved in the process, such as ionization energy, electron affinity, and lattice energy.

## 2. What is the role of lattice energy in the Born-Haber Cycle?

Lattice energy is the energy released when ions in a crystal lattice come together to form a solid. In the Born-Haber Cycle, it is a key factor in the formation of a chlorine atom as it represents the energy released when a solid crystal of sodium chloride (NaCl) is formed from gaseous ions of sodium (Na+) and chlorine (Cl-).

## 3. How does electron affinity play a role in the Born-Haber Cycle?

Electron affinity is the energy change that occurs when an atom gains an electron. In the Born-Haber Cycle, electron affinity is a crucial step in the formation of a chlorine atom as it represents the energy released when a chlorine atom gains an electron to form a chloride ion (Cl-).

## 4. What is the significance of ionization energy in the Born-Haber Cycle?

Ionization energy is the energy required to remove an electron from an atom. In the Born-Haber Cycle, ionization energy is an important factor as it represents the energy needed to remove an electron from a sodium atom (Na) to form a sodium ion (Na+).

## 5. What other factors are taken into account in the Born-Haber Cycle?

In addition to lattice energy, electron affinity, and ionization energy, the Born-Haber Cycle also considers other factors such as enthalpy of sublimation, enthalpy of fusion, and enthalpy of vaporization. These are the energy changes that occur when a solid substance changes to a gas or vice versa, and they play a role in the formation of a chlorine atom.

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