Exploring the Mystery Of Lattice Energy Under Standard Conditions

In summary: What about bond energy and atomisation enthalpy? Are those quantities thermodynamic? Also, on what basis do I judge whether or not a quantity is thermodynamic?Bond energy and atomisation enthalpy are both thermodynamic. However, they are not directly related to each other. That said, they are both important concepts to understand for understanding thermodynamics.
  • #1
PFuser1232
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My A level Chemistry textbook defines Lattice Energy as "the enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions"; a definition which I can't fully grasp because of the "standard conditions" part. How can gaseous ions exist under standard conditions?
 
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  • #2
That's a hypothetical point of reference. More precisely you extrapolate the enthalpy of a gas of the ionic compound from it's ideal behaviour at very small pressure to the value at 1 bar. So effectively you calculate with a gaseous phase at infinitely small pressure, but (more so for entropy than enthalpy) you have to fix units.
 
  • #3
DrDu said:
That's a hypothetical point of reference. More precisely you extrapolate the enthalpy of a gas of the ionic compound from it's ideal behaviour at very small pressure to the value at 1 bar. So effectively you calculate with a gaseous phase at infinitely small pressure, but (more so for entropy than enthalpy) you have to fix units.

What about temperature? How can gaseous ions exist at room temperature? Also, just to be clear, does this apply for ionisation energy and electron affinity as well?
 
  • #4
MohammedRady97 said:
What about temperature? How can gaseous ions exist at room temperature? Also, just to be clear, does this apply for ionisation energy and electron affinity as well?

Before discussing this any further, I want to point out that this question is probably not too relevant for what you are about (I suppose Born Haber cycles), as the ionization enthalpy does depend only to a minor extent on temperature and pressure.
This having been said, let's go on:
In principle there is always a gaseous phase at equilibrium with a solid. At low temperatures it will behave like an ideal gas as pressure is very low. Hence it is an easy exercise to extrapolate the ideal gas law to any pressure and temperature you like.

Ionisation energy and electron affinity aren't thermodynamic quantities, so they are independent of temperature and pressure.
 
  • #5
DrDu said:
Before discussing this any further, I want to point out that this question is probably not too relevant for what you are about (I suppose Born Haber cycles), as the ionization enthalpy does depend only to a minor extent on temperature and pressure.
This having been said, let's go on:
In principle there is always a gaseous phase at equilibrium with a solid. At low temperatures it will behave like an ideal gas as pressure is very low. Hence it is an easy exercise to extrapolate the ideal gas law to any pressure and temperature you like.

Ionisation energy and electron affinity aren't thermodynamic quantities, so they are independent of temperature and pressure.

So is my textbook wrong in defining (the first) electron affinity as "the enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions under standard conditions."?
 
  • #6
No, that's a correct definition. As DrDu stated several times, we EXTRAPOLATE to standard conditions. Otherwise we would have numbers that are not comparable.
 
  • #7
Borek said:
No, that's a correct definition. As DrDu stated several times, we EXTRAPOLATE to standard conditions. Otherwise we would have numbers that are not comparable.

Yes, I am quite familiar with this now. But I was referring to his statement regarding the fact that ionization energy and electron affinity are not thermodynamic quantities.
 
  • #8
DrDu said:
Before discussing this any further, I want to point out that this question is probably not too relevant for what you are about (I suppose Born Haber cycles), as the ionization enthalpy does depend only to a minor extent on temperature and pressure.
This having been said, let's go on:
In principle there is always a gaseous phase at equilibrium with a solid. At low temperatures it will behave like an ideal gas as pressure is very low. Hence it is an easy exercise to extrapolate the ideal gas law to any pressure and temperature you like.

Ionisation energy and electron affinity aren't thermodynamic quantities, so they are independent of temperature and pressure.

What about bond energy and atomisation enthalpy? Are those quantities thermodynamic? Also, on what basis do I judge whether or not a quantity is thermodynamic?
 

1. What is lattice energy under standard conditions?

Lattice energy under standard conditions is the amount of energy released or absorbed when a crystal lattice is formed from its constituent ions in their gaseous state at standard temperature and pressure.

2. How is lattice energy calculated?

Lattice energy is calculated using the Born-Haber cycle, which takes into account the formation of ions from atoms, the transfer of electrons to form ions, and the formation of the crystal lattice. The final value is determined by taking the difference between the energy required to break the lattice and the energy released when the lattice is formed.

3. What factors affect lattice energy?

The magnitude of lattice energy is influenced by the charges of the ions, their sizes, and the distance between them. Generally, larger charges and smaller distances result in higher lattice energy.

4. Why is lattice energy important in chemistry?

Lattice energy is important in understanding the stability and properties of ionic compounds. It also plays a role in the melting and boiling points of these compounds, as well as their solubility and conductivity.

5. How does temperature affect lattice energy?

Lattice energy is a function of temperature, with higher temperatures resulting in lower lattice energy. This is because the thermal energy can overcome the attractive forces between ions, weakening the lattice. However, this effect is only significant at very high temperatures.

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