Born Haber Cycles and Enthalpy changes

What are Born Haber cycles used for?

Used to determine the enthalpy change for an alternative indirect pathway as lattice enthalpies cannot be measured directly

What is ion polarisation?

When in an ionic lattice the positive charge on the cation may attract the electrons in the anion towards it resulting in a distortion of the anions electron cloud therefore causing the anion to lose its spherical shape

What is polarising power?

The ability of a cation to polarise nearby anions

What does greater polarisation lead to?

More covalent bonding

3 factors that affect ion polarisation?

1. Small, highly charged cations have greater polarisation power than larger lower charged ones because their positive charge is more concentrated increasing their attraction to the anions electrons

2. Large anions with high charge are more easily polarised than smaller lower charged ones because their electrons are further from the nucleus and experience greater repulsion and attraction to cations

3. When a highly polarising cation and easily polarised anion are combined the anions electron cloud is significantly drawn towards the cation and sufficient polarisation results in a partially covalent bond

What 2 things happen when an ionic solid dissolves in water?

1. The ionic bonds are broken to form gaseous ions. The process is endothermic and the enthalpy change is equal in magnitude but opposite in sign to the lattice enthalpy

2. New bonds are formed between the gaseous ions and water molecules to form hydrated ions. This process is exothermic and the enthalpy change is called the enthalpy of hydration

What is enthalpy change of solution?

the enthalpy change when 1 mole of solute is dissolved in sufficient water to form a very dilute solution and is calculated by the sum of endothermic lattice breaking and exothermic hydration

What is enthalpy change of hydration?

The enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions

Why do soluble substances usually have exothermic enthalpies of solution?

Because for substances to dissolve the energy released from hydration must be similar to or greater than the energy required to break up the lattice

What is percentage yield?

The amount of product you actually make as a percentage of the amount you should theoretically make actual/ theoretical x 100

What is atom economy?

The mass of the product you want as a percentage of the mass of all the products you make

What is enthalpy change of reaction?

The enthalpy change when the amounts of reactants shown in the equation react under standard conditions to give the products in their standard states

What does FAIL stand for?

Formation Ionisation Atomisation Lattice enthalpy

What is lattice enthalpy?

The energy released to form 1 mole of a solid ionic lattice from its gaseous ions under standard conditions

What is lattice enthalpy of dissociation?

The standard enthalpy change when 1 mole of solid ionic compound is dissociated into its gaseous ions

What is standard enthalpy of atomisation?

The standard enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard state under standard conditions

What is bond dissociation enthalpy?

The energy needed to break 1 mole of the bond to give separated atoms in gas state

What is first ionisation energy?

The standard enthalpy change when one mole of gaseous atoms is converted into one mole of gaseous ions each with a single positive charge

What is first electron affinity?

The standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single negative charge