enthalpy

Definition of first ionization energy

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous +1 ions

Enthalpy of atomization

The enthalpy change when one mole of gaseous atoms is formed from its elements in its standard state.

First electron affinity

The energy released when one mole of gaseous atoms gains one mole of electrons to form one mole of 1- ions

Enthalpy of formation

the enthalpy change when one mole of substance is formed from its elements under standard conditions with all reactants and products in their standard states.

Define Bond enthalpy

The enthalpy change when one mole of gaseous covalent bonds are broken

Lattice Enthalpy of formation

The energy released when one mole of an ionic solid compound in its standard state is formed from its constituent gaseous ions.

In a Born-Habor cycle what is usually on the right side?

Lattice Enthalpy formation/dissociation of the compound and electron affinity

Enthalpy of hydration

The enthalpy change when one mole of gaseous ions dissolves in water to form one mole of hydrated ions under standard conditions.

E.g Na+ + aq → Na+ (aq) \Delta H hydration= negative

Cl-(g) → Cl - (aq)

Enthalpy of solution

The Enthalpy change when one mole of ionic compound is dissolved in water to form separate aqueous ions under standard conditions

E.g NaCl (s) → Na+ ions(aq) + Cl- ions(aq)

Equation with lattice Enthalpy of formation and hydration and solution

Enthalpy of lattice= sum of Enthalpy of hydration - Enthalpy of solution

Born-haber cycle

Is an Enthalpy/hess cycle composed of all the Enthalpy changes involved in the formation of 1 mole of ionic compound from its constituent elements in their standard states.

Explain the difference between the Theoretical and experimental values of lattice Enthalpy

Theoretical values assume that the compound is purely ionic

Experimental values are usually higher than the theoretical value, because the lattice Enthalpy is greater due to polarization.

So there is a large discrepancy between them

What two things affect the Enthalpy of hydration?

The size and charge of the molecule

What 2 assumptions in the perfect ionic model?

• All the ions are perfectly spherical- even charge distribution

• The ions display no covalent character (only electrostatic attraction)

Suggest 2 ways covalent character occurs in ions

• The two ions have varying sizes

• The two ions have varying charges

  both cause uneven charge distribution

Explain why aluminum iodide exerts covalent character while sodium chloride doesn’t

There is a larger difference in charge between the Ag 3+ ions and the I- ions

Compared with Na+ and Cl- ions

The iodide ions have a much greater ionic radius, so the electron density is pulled towards the positive Ag 3+ cations

This causes uneven charge distribution which causes covalent character

Explain why the experimental and theoretical values of lattice energy are significantly different between calcium iodide. When theoretical=-1905 kJMol-1 experimental=-2074 kJMol-1

Because calcium iodide has polarization in the ionic bonds causing it to exhibit covalent characteristics. Causing the bonds to deform and become polarised. Therefore has a greater lattice Enthalpy. The theoretical value assumes Calcium Iodide is 100% ionic compound

Define rate of reaction

The change in concentration/amount of reactant or product per unit of time

Formula for rate of reaction

Amount of reactant used or product made divided by time

What are the 2 factors needed for collision theory

For a reaction to occur the particles must collide in the right direction and have a minimum amount of KE

Define activation energy

The minimum amount of energy required for a reaction to occur

What is the formula to work out the enthalpy of solution?

Snakes produce rice

Enthalpy of solution= Enthalpy of formation of products (aqueous ions) - Enthalpy of formation reactants of solid and solvent (H2O)

Breaking bonds is….

Endothermic

Because energy is needed to break the bonds

Making bonds is…

Exothermic

Because energy is made from forming bonds

BENDO MEXO or clapping produces a sound so forming a bond is exothermic

Define Lattice enthalpy of dissociation

The enthalpy change when one mole of a solid ionic compound is broken down into its gaseous ions under standard conditions

Is lattice enthalpy of dissociation endo or exo?

Endothermic because you are breaking ionic bonds

Is lattice formation enthalpy endo or exo?

Exothermic because you are forming ionic bonds

Define Hess’s law

The enthalpy change is independent of the route taken