Lattice enthalpy Flashcards
Define lattice enthalpy
The enthalpy change associated with the formation of one mole of an IONIC compound from its gaseous ions under standard conditions
What is the symbol for lattice enthalpy
ΔLeHϴ
What symbol accompanies lattice enthalpy?
-
Why is lattice enthalpy always negative?
It represents the formation of bonds which releases energy and so is exothermic
Write an equation to represent the lattice enthalpy of NaCL
Na+ (g) + Cl- (g) —-> NaCl(s)
What is the definition of enthalpy of formation?
The enthalpy change that accompanies the formation of one mole of a substance from its elements under standard conditions with all reactants and products in their standard states
What is the definition of 1st ionisation energy?
The amount of energy required to remove one electron from each atom in one mole of gaseous atoms OF AN ELEMENT to form one mole of gaseous 1+ ions
Write an equation for 1st ionisation energy
Na(g) —–> Na+ (g) + e-
What is the sign of ionisation energy?
+
Why is ionisation always positive?
Energy is required to pull the electron being removed away from the nucleus
As more electrons are removed what happens to the value of IE and why?
The value increases
As more electrons are removed the remaining electrons are pulled in closer to the nucleus and so more energy is required to remove the electrons
What is the definition of enthalpy of atomisation?
The enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
What is the sign for enthalpy of atomisation?
Always +
Why is the sign of enthaply of atomisation always +?
Bonds holding atoms together in their standard states must be broken
What is the definition of 1st electron affinity?
Th energy change that accompanies the addition of one electron to each atom in one mole of atoms of an element on gaseous form to form one mole of gaseous 1- ions
Is 1st Electron affinity exothermic?
Yes
Why is 1st electron affinity exothermic?
An electron is being added and will be attracted to the nucleus
Are subsequent electron affinities exothermic?
No
Why are subsequent electron affinities endothermic?
Electrons are being added to a negatively charged ion, and it is necessary to overcome the repulsion
From the bottom left hand side round to the bottom right hand side, what is the order of enthalpy changes?
- Formation
- Atomisation
- 1st ionisation energy
- any subsequent ionisation energies
- atomisation
- 1st electron affinity
- any subsequent electron affinities
- lattice enthalpy
Define enthalpy of hydration
The enthalpy change when one mole of isolated gaseous ions is dissolved in water under standard conditions
Define enthalpy change of solution
The enthalpy change when one mole of a substance is completely dissolved in water under standard conditions
What is the symbol for enthalpy change of solution?
ΔsolHϴ
What is the symbol for enthalpy change of hydration?
ΔhydHϴ
Is the enthalpy change of solution endothermic or exothermic?
Either
Is the enthalpy change of hydration endothermic or exothermic?
Exothermic
Why is the enthalpy change of hydration exothermic?
Bonds are being formed between ions and water
Are the lattice enthalpies of larger ions more or less exothermic?
Less
Why do larger ions have a less exothermic lattice enthalpy?
- the electrostatic attraction between the ions is weaker
- because the ions have a lower charge density
How is charge density calculated?
charge/volume
Are the lattice enthalpies of more highly charge ions more or less exothermic?
More
Why do more highly charged ions have a more exothermic lattice enthalpy?
- the electrostatic attraction between the ions is stronger
- because the charge density is higher
Do smaller ions have a more or less exothermic value of enthalpy of hydration?
More
Why do smaller ions have a more exothermic enthalpy of hydration?
- smaller ions have larger charge densities
- so attract water molecules more strongly
Do ions with a smaller charge have more or less exothermic enthalpies of hydration?
Less
Why do ions with a smaller charge have a less exothermic enthalpy of hydration?
- the ions have smaller charge densities
- so they cannot attract water molecules as strongly
