Paper 3B Part1

enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states

enthalpy change when one mole of compound is formed from its constituent elements under standard conditions

enthalpy change when one mole of substance is burnt completely in excess oxygen under standard conditions

• Loss of an electron(s) by an element2. Gain electrons by a second element3. Attraction between positive and negative ions

Ionisation Energy – Na  e- + Na+ +496kJmol-1Electron Affinity – e- + Cl  Cl- -349kJmol-1Lattice Enthalpy – Cl- + Na+  NaCl -766kJmol-1

.The enthalpy change when one mole of electron is added to one mole of atoms in the gaseous phase to form one mole of -1 ions

.Repulsion between two negatively charged things requires energy so exothermic

.ΔHlatt is the enthalpy change when 1 mole of ionic substance is formed from its gaseous ions under standard conditions

more exothermic the greater the ionic bonding

Cannot be measured directly as cannot form one mole of ionic lattice from gaseous ions

Charge – .The greater the charge on the ions, the stronger the attraction – therefore, more exothermic lattice enthalpySize – .Smaller ions can pack together more tightly, therefore there is greater attraction and more exothermic lattice enthalpy

.They have decreasing charge densities.Mg2+ is a smaller ion than Ba2+ , so the +2 charge occupies a smaller volume – this means Mg2+ has a higher charge density than Ba2+.Mg2+ can distort the electron clouds within the CO32- ion (called polarisation), this weakens the covalent bonding in the ion and reduces its decomposition temperature

L.E = FORMATION – sum(ATOM + I.E + E.A)orL.E = FORMATION – sum(REST)

Born Haber cycles can be used to calculate a measure of ionic bond strength based on experimental data

check notes or google

check notes or google

check notes or google

DeltasolutionH is the enthalpy change when one mole of ionic compound is completely dissolved in water under standard conditions.e.g. NaCl(s)  Na+(aq) + Cl-(aq)

• Delta Hhydration¬ is the enthalpy which takes place when one mole of gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions- Na+(g) + aq  Na+(aq)

These are exothermic as bonds are formed between the ions and water molecules

Charge – the higher charge on the ion, the greater the attraction for the H2O molecules, therefore a more exothermic hydrationSize – smaller ions have a greater charge density compared to the larger ions, this creates a greater attraction for H2O molecules, therefore a more exothermic hydration

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lattice enthalpy + enthalpy of solution = sum of the enthalpy of hydrations

A chemical reaction will proceed if the products are energetically more stable than the reactants