Thermodynamics

• Define lattice enthalpy of formation.


  The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions.
• Define lattice enthalpy of dissociation


  The enthalpy change when 1 mole of a solid ionic compound is completely dissociated from into its gaseous ions.
• Define bond dissociation enthalpy. Give an example.


  The enthalpy change for breaking 1 mole of a particular covalent bond in the gaseous state
• enthalpy of atomisation of an element

  The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state under standard conditions.
• First ionisation energy.

  The enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms of an element to form one mole of gaseous 1+ (cat)ions are formed.
• Second ionisation energy.

  The enthalpy change when 1 mole of electron is removed from 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ (cat)ions.
• First electron affinity. define

  enthalpy change when one mole of gaseous 1- (an)ions is formed from 1 mole of gaseous atoms
• Second electron affinity.

  enthalpy change when one mole of gaseous 2- (an)ions is formed from 1 mole of gaseous 1- ions.
• enthalpy change of hydration

  The enthalpy change when one mole of aqueous ions is formed from 1 mole of gaseous ions
• enthalpy change of solution.

  The enthalpy change when one mole of an ionic substance dissolves in enough solvent to from an infinitely dilute solution.
• enthalpy change of formation

  The enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions
• enthalpy of combustion

  The enthalpy change when 1 mole of a substance undergoes complete combustion in excess oxygen with all substances in their standard states under standard conditions.
• Bond enthalpy

  The enthalpy change for breaking 1 mole of a particular covalent bond in the gas phase to form gaseous atoms
• define the enthalpy change of atomisation of a compound.

  The enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms.
• enthalpy change

  Heat energy change at constant pressure
• Why is the enthalpy change for second electron affinity endothermic (positive)

  The negative ion / species repels the electron being added
• why is the enthalpy change for second ionisation energy much larger than first

  Electron more strongly attracted

  as it is nearer to the nucleus or attracted to the X+ ion
• Suggest one reason why this value is different from your answer (bond enthalpies) make it specific to that question)

  • mean bond enthalpies are not the same as the actual bond enthalpies in CO2
• suggest one environmental advantage of manufacturing methanol fuel by this reaction

  • carbon dioxide is used up in this reaction
• suggest why the lattice enthalpy of silver chloride value using the ionic model is different

  • model assumes the ions are spherical and in a lattice
  • the calculated value is smaller than the cycle value
  • indicating some covalent character
• suggest why the reaction s occurs at room temperature even though the reaction is endothermic

  • For the reaction gibbs free energy must be lower than 0
  • change in entropy is positive and large asa gas is evolved
  • T*S is larger than Change un enthalpy is negative
• explain why the cl-cl bond is greater than the br-br bond

  • cl is a smaller atom
  • so attraction between nucleus’s and to bond pair is stronger
• meaning of perfect ionic model

  • ions can be regarded as perfect spheres
  • with no covalent interaction
• suggest why the theoretical enthalpy of lattice dissociation of AgCl is greater than expected

  AgCl id greater

  • silver chloride has covalent character
  • forces in the lattice are stronger than pure ionic attractions
• Suggest how different the theoretical enthalpies of lattice dissociation for AgCl and AgBr

  • silver chloride is greater
  • chloride ions are smaller than bromide ions
  • they are attracted more strongly to silver ions
• describe the steps o determine an accurate minimum temperature that is not influenced by heat in surroundings ( temperature decrease)

  • start clock then potassium chloride is added to water
  • record temperature every minute for 5 minutes
  • plot graph of temperature vs time
  • extrapolate back to time of mixing (0) and determine temperature
• suggest why lattice enthalpy of dissociation is different between MgCl and CaCl2

  • magnesium ion is smaller than calcium ion
  • attracts chloride ion more strongly
  • stronger ionic bonding
• Enthalpy of atomisation

  • enthalpy change for the formation of 1 mole of gaseous atoms
  • from the element
• Lattice dissociation enthalpy

  Enthalpy to change to separate 1 mole of an ionic compound into its component gaseous ions
• Electron affinity

  • enthalpy change when 1 mole of gaseous atoms form one mole of gaseous negative ions
• Explain why the hydration enthalpy if fluoride is more negative than the hydration enthalpy of the chloride ion

  • Fluoride ion smaller than chloride ions
  • negative charge attracts delta positive hydrogen in water more strongly
• Pure ice can look pale blue when illuminated by white light suggest why

  • light is absorbed by the ice
  • blue light is transmitted / reflected
• use knowledge of bonding to suggest why centrally change is positive for a ice to liquid water

  • because of the hydrogen bonds between water molecules
  • enegy must be supplied to break some of those bonds
• Suggest one reason why the first electron affinity of oxygen is an exothermic process / negative

  there is attractive forces between the nucleus of an oxygen atom and an external electron
• Platinum acts as a hetereogenous catalyst in a reaction between ammonia and oxygen, describe alternate route using catalyst

  • reactants adsorb onto the surface of catalyst (platinum)
  • Bonds within the reactant molecules become weaker
  • New bonds form between the reactants held close together on the catalyst surface
  • desorption of the product as the bonds between the product and catalyst weaken
• In terms of forces acting on particles suggest why the first electron affinity of oxygen is an exothermic process

  • there is an attractive force between the nucleus of an oxygen atom and the outer electron
• Suggest why the eelectron affinity of fluorine has a negative value

  • There is an attraction between the positive nucleus and the added electron
  • Energy is released when the electron is gained
• Suggest why the value for the enthalpy of hydration for chloride ions is more negative than that for the bromide ion

  • Chloride ions are smaller than bromide ions
  • So the force of attraction between chloride ions and water is stronger
  • Chloride ions attract the δ+ delta positive H of water
• suggest why the hydration of the chloride in is an exothermic process

  • Water is polar / water has H (delta positive) δ+
  • Chloride ion attracts the H in water molecules
• Draw where boiling point is

  Where vertical section of l 2 starts