Lattice Energy - Meaning, Definition, Factors, Differences, Calculation, FAQs

In the field of chemistry, lattice energy is defined as the energy associated with the separation of one mole of ionic solid into its gaseous ions. Thermodynamically, therefore, the value that will be obtained for lattice energy will become very crucial in explaining or demonstrating the wide range of properties for the ionic compounds formed through electrostatic attraction between positively charged cations and negatively charged anions. It can, however, also be described as the energy released when gaseous ions react by combining in the formation of an ionic solid. The value is hence indicative of the strength of the ionic bonds holding the compound. The lattice energy is generally expressed in kJmol. As in the value of lattice energy, there are many factors and influences on the charge of the ions and interionic distance. Lattice energy is directly proportional to the stability of the compound that could be formed by the cation and the anion; it is simply so because stronger ionic interactions will have higher melting and boiling points. This is of most interest, not only as a well-based theoretical exercise in chemistry but also confers realistic utility and is further used in varied fields, sometimes that of materials science or even in a bio or environment-related context. This paper will further bring out the identification of the lattice energy and explain the same. This will be followed by types and determinants of lattice energy with examples to make it clear on the considerations. Then, a third section shall finally show the relevant real-life issues and importance in academic areas rather than showing their application in life and studies.

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Lattice Energy Understanding

Lattice energy is the energy change that accompanies the formation of one mole of an ionic crystalline solid from its free gaseous ions.

It can be considered in two equivalent methods. It can either be said to be the energy that is needed to separate ions in an ionic solid from each other in the gaseous state, which is an endothermic course of action, or it can be described as the energy that is released from the two coming together to yield the solid, which is an exothermic course of action.

The sign of this lattice energy may vary from negative to positive, positive or negative, depending on the manner a corresponding process is run.

Because the lattice energy can be in a direct proportionality related to the strength of an ionic bond, then the higher the lattice energy, the higher the attraction of the ions, hence the stability of the compound. Two general factors are believed to affect the overall strength of lattice energy: the charge on the ions and the separation distance between the ions. Coulomb's Law simply states that the electrostatic force of attraction between charged particles is directly proportional to the magnitude of a charge and inversely proportional to the distance that separates those charges. Hence, lattice energies are higher for those ionic compounds with higher charges and smaller ionic radii.

Calculations of lattice energy are most of the time heterogeneous, and demands are very high since they are experimentally indirect, being acquired from the Born-Haber cycle. The formation of an ionic compound is simply the summation of a set of steps in the Born-Haber cycle. In this process, an individual chemist can easily calculate the range of changes in energy ending up being every step of the way and finally being captivated by the energy in the stick.

The lattice energy of a compound is a measure of the strength of this attraction. The lattice energy (ΔH_lattice) of an ionic compound is defined as the energy required to separate one mole of the solid into its component gaseous ions. For the ionic solid MX, the lattice energy is the enthalpy change of the process:

MX(s) $\longrightarrow$ Mⁿ⁺(g)+X^n-(g) $\Delta H_lattice$

The lattice energy ΔHlattice of an ionic crystal can be expressed by the following equation:

$\Delta \mathrm{H}_{\text {lattice }}=\frac{\mathrm{C}\left(\mathrm{Z}^{+}\right)\left(\mathrm{Z}^{-}\right)}{\mathrm{R}_0}$

in which C is a constant that depends on the type of crystal structure; Z⁺ and Z^– are the charges on the ions, and Ro is the interionic distance. Thus, the lattice energy of an ionic crystal increases rapidly as the charges of the ions increase and the sizes of the ions decrease.

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The Born-Haber Cycle

It is not possible to measure lattice energies directly. However, the lattice energy can be calculated using the equation given in the previous section or by using a thermochemical cycle. The Born-Haber cycle is an application of Hess’s law that breaks down the formation of an ionic solid into a series of individual steps:

• ΔH_f°, the standard enthalpy of formation of the compound

• IE, the ionization energy of the metal

• EA, the electron affinity of the nonmetal

• ΔH_s°, the enthalpy of sublimation of the metal

• D, the bond dissociation energy of the nonmetal

• ΔH_lattice, the lattice energy of the compound

The figure given below shows the Born-Haber cycle for the formation of solid cesium fluoride.

The Born-Haber cycle shows the relative energies of each step involved in the formation of an ionic solid from the necessary elements in their reference states.

For Caesium fluoride, the lattice energy can be calculated using the given values as follows:

$\Delta H_{\text {lattice }}=(553.5+76.5+79.4+375.7+328.2) \mathrm{kJ} / \mathrm{mol}=1413.3 \mathrm{~kJ} / \mathrm{mol}$

Types and Factors Influencing Lattice Energy Lattice energy may, therefore, be categorized using the nature of the ionic compounds involved and the type of interaction between ions. Some common forms of lattice energy include:

1. Formation Lattice Energy: The energy belonging to the reaction when gaseous ions come together to form one mole of an ionic solid. Since this process is exothermic, the lattice energy change is negative.

2. Dissociation Lattice Energy: The energy changes when one mole of an ionic solid breaks up into its constituent gaseous ions. It is an endothermic process, so lattice energy is always positive.

The lattice energy depends on:

Ionic charge: In case the charge of the ions increases then electro-static attraction and hence lattice energy of the ionic solid increases. For instance, the lattice enthalpy of magnesium oxide is higher compared to sodium chloride due to the reason that Mg²⁺ and O²⁻ have higher charges compared to Na⁺ and Cl‾.

Ionic Radius: The smaller the ions, the closer the ions get to one another, increasing the attraction forces between them and hence lattice energy. For example, lithium fluoride, due to its size, has lower lattice energy than potassium bromide. This is because lithium ions are smaller in comparison to potassium ions and offer better interaction.

Thus the knowledge of these factors assumes prime importance in understanding the different properties of ionic compounds like solubility, melting points, and stabilities.

Related Topics Link

• Crystallization
• Bcc Fcc Primitive Cubic Unit Cell
  
• Amorphous solid
• Frenkel Defect

Real-Life Applications of Lattice Energy

Furthermore, the applications of lattice energy are of much importance both at the academic levels of research and in day-to-day life.

The importance of information on lattice energy gets underlined for two things: the synthesis of new ionic compounds having some desired properties.

Most of the fabrication processes for ceramics and glasses strongly rely on lattice energy because these materials are mainly composed of ionic, and hence strong compounds. In turn, such compounds are held together by strong ionic bonds and are thus very stable and robust. Lattice energy, lying at the very heart of chemical education, is one of the myriad central concepts bared to the student in chemistry to introduce him to some fundamentals with ionic bonding and crystal structures. Far too often, though, this is done using the Born-Haber cycle—where lattice energy is a part of the process—in efforts to explain to advanced students just how it is possible to calculate and interpret energy changes associated with the formation of an ionic compound.

The energy also contributes biochemically to a multitude of biochemical systems. This can be noted, in a way, by the stability of the ionic compounds within the biological fluids, containing ions of sodium and potassium, and supporting quite several cellular functions, checking the transmission of impulses. Control of ions in this manner, thus controlled through lattice energies, gets to be very important in muscle contractions and neural signaling. Another application is in the field of environmental science, particularly in the areas of solubility and precipitation reactions. The lattice energies of several ionic compounds assist in predicting their properties in natural water systems, right from nutrient availability in the ecosystems to the creation of mineral deposits.

In a nutshell, that is lattice energy—the concept of chemistry that, other than its pivotal understanding in ionic compounds, stretches far out to include quite expansive applications in other scientific and practical genres.

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For a better understanding of the topic and to learn more about Lattice Energy with video lesson we provide the link to the

YouTube video:

Some Solved Examples

Example 1: Lattice energy is inversely proportional to the sum of radii of

1)radius of anion

2)radius of cation

3) (correct)sum of radii of ions

4)sum of radii of atoms

Solution

As we have learned,

Lattice Energy(Ionic Bond Energy) $\propto \frac{\text { Cation Charge } \cdot \text { Anion Charge }}{\text { Cation Radius }+ \text { Anion Radius }}$

Example 2: Lattice energy is always

1)exothermic

2) (correct)endothermic

3)ectothermic

4)hypothermic

Solution

As we have learned, Lattice energy is the energy required to completely separate one mole of solid ionic compound into its constituent gaseous ions.

As the definition implies, this process will always be endothermic; thus, the value for lattice energy will be positive.

Hence, the answer is the option (2).

Example 3: A type of enthalpy cycle that is used to calculate lattice energy is

1)Hess's Law

2) (correct)Born-Haber cycle

3)Haber process

4)Contact process

Solution

Born Haber's cycle is used to determine the value of lattice energy.

Hence, the answer is the option (2).

Example 4: Which one of the following has the largest lattice energy?

1) MgF₂
2) NaF
3)CaF₂
4) (correct) AlF₃

Solution

Lattice energy is directly proportional to charge and inversely proportional to size of ions.In MgF₂ we haveMg²⁺ ion, In NaF we have Na⁺ ion, In CaF₂ we have Ca²⁺ ion, InAlF₃ we have Al³⁺ ion. So, if we look on charges then AlF₃ has largest lattice energy. Hence, the answer is the option (4).

Summary

It describes the energy that occurs, in either the formation or dissociation process of the ionic compounds. It focused on both the formation and the dissociation points of view, in addition to the factors that depend on such things as ionic charge and radius.

The application is not theoretical in chemistry but has an impact on materials science, biology, and environmental reasons.

Lattice energy finds an application in materials science at a more central, core level, in the structure of stable ionic compounds in ceramics and glasses for durability. In fact, lattice energy even finds applications in environmental studies, in an attempt to calculate solubility and reactivity of ionic compounds in natural systems. Lattice energy is abstract and therefore forms part of life. Much of what we do in life falls under the impact of this nature, from the small to the huge. The role of lattice energy in the advancement of sciences is huge. In understanding lattice energy, one opens up avenues to predict the properties and behavior of ionic compounds—this is crucial information in the innovation of technologies, medicine, and the sustainability of the environment.

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