Energetics II

Enthalpy change when 1 mol of an Ionic lattice is formed from isolated gaseous atoms under standard conditions

Is a measure of Ionic bond strength The more negative the lattice energy the stronger the bond

The higher the charge on the ions,the more energy is released when an Ionic lattice forms This is due to stronger electrostatic forces of attraction The smaller the Ionic radius of ions involved,the more exothermic the lattice energy is

The enthalpy change when one mole of aqueous ions are formed from their gaseous ions under standard conditions E.g K+(g)+H20>K+(aq)

Exothermic-as making bonds is an exothermic process

The enthalpy change when one mole of an Ionic substance dissolves in water

Ionic lattice breaks down into gaseous ions Ions are hydrated(enthalpy of hydration)

This is: Enthalpy change of hydration-enthalpy change of lattice

This means it’s exothermic and the energy required to separate the solute into its constituent ions is less than the energy given off when ions are hydrated Use the equation

This is endothermic and the amount of energy required to separate the solute into constituent ions is greater than energy given off when ions are hydrated

The smaller the size of ions the greater the enthalpy of hydration-This is because small ions exert more attraction on water molecules and more energy is released when hydrated.

As charge on the ions increases it has a greater attraction for water molecules This is because more highly charged ions exert more attraction on water molecules and more energy is released when these are hydrated

Some Ionic compounds have covalent characteristics Theoretical ECOL does not account for this whereas experimental does This means theoretical is less exothermic that experimental

The higher the charge of the cation-the greater polarising power so more covalent character The smaller the ion the greater charge density so more polarising The greater the size the more polarisable it is

Very small as it has one electron shell so small Ionic radius Small ions exert more attraction so more energy is released

If enthalpy change of solubility is negative(exothermic)than it is soluble If it is slightly endothermic for example between 0-10KJ per mol it is also soluble

Energy change when one mole of an Ionic solid is formed from its gaseous ions

Energy change when one mole of electrons is gained by one mole of gaseous atoms of an element to form one mole of gaseous ions under standard conditions

Enthalpy change when 1 mole of gaseous atoms is formed from its elements under standard conditions

Polarisation of an ion refers to the electron cloud distortion of ions

Smaller cations are more effective at polarising an anion Polarising power increases with the charge of the cation increasing

Theoretical enthalpy assumed that its a perfect spherical Ionic model with no distortion Experimental takes in account borne haber cycles

1 mol of substance 100Kpa 298K

High activation energy Rate of reaction is too slow