Module ? Lattice enthalpy

What is enthalpy change of formation?

When 1 mole of a compound is formed from its elements in their standard states under standard conditions

What is lattice enthalpy of formation?

The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard condition

What is enthalpy of 1st ionisation?

The enthalpy change when 1 mole of gaseous 1+ ions are made from 1 mole of gaseous atoms

How does the size of the charge (number) on the ion affect the strength of the ionic bonding?

The bigger the charge the stronger the electrostatic attraction between ions

More energy is required to overcome these forces so they have a high melting and boiling point

E.g sodium chloride

How does the size of the ion (ionic radius) affect the strength of the ionic bond

The smaller the ion the stronger the electrostatic attraction between ions

Smaller ions can pack together more closely and more energy is required to overcome the stronger forces.

So the mp and bp are higher

What is electron affinity?

The enthalpy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous negative atoms

Why is 2nd electron affinity endothermic?

Because energy is needed to add an electron to a negative ion. Repulsive forces between 2 negative species require energy to overcome

What is enthalpy change of solution?

the enthalpy change when 1 mole of an ionic substance is dissolved in the minimum amount of solvent to ensure no further enthalpy change is observed upon further dilution

What must happen for a substance to dissolve?

1. Substance-bonds must break (endothermic)

2. New bonds form (exothermic)

What is enthalpy of hydration?

Enthalpy change when 1 mole of aqueous ions is made from 1 mole of gaseous ions

What is the enthalpy change of disassociation?

the enthalpy change when one mole of an ionic solid lattice is separated into its gaseous ions

How to calculate enthalpy change of solution?

By doing the enthalpy change of disassociation and then the enthalpy change of hydration

How does calculating the enthalpy change of solution work?

1. Break the solid lattice up into its gaseous ions (lattice disassociation)

2. Dissolve the gaseous ions in water (enthalpy change of hydration)

What is hydration?

When water molecules surround the ions and hydrogen bonds form whcih break down the structure and dissolve it.

If bonds are formed between the ions and water what is it called?

The ions are hydrated

What must happen for the ions to be hydrated?

The new bonds formed must be the same strength or greater than those broken

What are the 2 things that can affect enthalpy change of hydration?

Charge and size of the ion

How does charge affect enthalpy change of hydration?

Ions with a higher charge attract water molecules more strongly bc the electrostatic attraction is stronger

More energy is released when the bond is made, which means they have a more exothermic enthalpy of hydration.

THE LARGER THE CHARGE THE GREATER THE ENTHALPY OF HYDRATION

How does Size of the ion affect enthalpy change of hydration?

Smaller ions have a higher charge density than larger ions

They can attract water molecules more strongly hence there is a more exothermic enthalpy of hydration.

THE SMALLER THE ION THE GREATER THE ENTHALPY OF HYDRATION