Chapter 22

• What is mean bond enthalpy?

  Average enthalpy change for breaking a bond
• What does standard enthalpy of formation (Δ_fH°) represent?

  Enthalpy change when one mole of substance forms
• What is the definition of standard enthalpy of combustion (Δ_cH°)?

  Enthalpy change when one mole of substance burns
• What does standard enthalpy of atomisation (Δ_atH°) indicate?

  Enthalpy change when gaseous atoms form from its elements
• What is first ionisation energy (Δ_iH°)?

  Enthalpy change when one mole of gaseous atoms loses an electron
• What does first electron affinity (Δ_eaH°) measure?

  Enthalpy change when gaseous atoms form negative ions
• What does the second electron affinity refer to?

  Gain of the second electron by an ion
• What is lattice enthalpy of formation (Δ_latH°)?

  Enthalpy change when solid ionic compound forms from gaseous ions
• What is lattice enthalpy of dissociation?

  Enthalpy change when solid ionic compound dissociates into gaseous ions
• What does standard enthalpy of hydration (Δ_hydH°) represent?

  Enthalpy change when gaseous ions form aqueous ions
• What is standard enthalpy of solution (Δ_solH°)?

  Enthalpy change when solute forms a solution
• What does lattice enthalpy measure?

  Strength of ionic bonding in a giant ionic lattice
• What process does lattice enthalpy involve?

  Ionic bond formation from separate gaseous ions
• Is lattice enthalpy an endothermic or exothermic change?

  It is an exothermic change
• What is the sign of the value for lattice enthalpy change?

  Always negative
• Why are ionisation energies considered endothermic?

  Energy is required to overcome attraction
• What does electron affinity measure?

  Energy to gain electrons
• How does ionisation energy differ from electron affinity?

  Ionisation energy measures energy to lose electrons
• What type of process is a second electron affinity?

  Endothermic
• Why is the second electron affinity endothermic?

  Negative ion repels the incoming electron
• What must happen to gain a second electron on a negative ion?

  Energy must be put in to force the electron
• How do water molecules interact with ionic compounds when salt dissolves in water?

  They break up the ionic lattice structure
• What type of attractions do water molecules overcome when dissolving salt?

  Strong electrostatic attractions
• What can the enthalpy change of solution be?

  Exothermic or endothermic
• Why is the attraction in ionic compounds described as existing in three dimensions?

  Because ions and water molecules are arranged in 3D
• What are the two processes that occur when a solid ionic compound dissolves in water?

  1. Ionic lattice breaks up into gaseous ions
  2. Gaseous ions interact with water to form hydrated ions
• What is the opposite energy change of lattice energy when an ionic compound dissolves?

  Breaking up the ionic lattice
• What is formed when separate gaseous ions interact with polar water molecules?

  Hydrated aqueous ions
• What is the energy change called when gaseous ions interact with water molecules?

  Enthalpy change of hydration
• What happens to the ionic lattice when a solid ionic compound dissolves in water?

  It is broken up
• What is the relationship between gaseous ions and the ionic lattice?

  Gaseous ions form the ionic lattice
• What factors affect lattice enthalpy?

  Ionic size and ionic charge

  
• How does ionic size affect lattice enthalpy?

  Smaller ions form stronger ionic bonds

  
• What is the effect of a lower charge ion on ionic bonds?

  Forms weaker ionic bonds
• What is the effect of a higher charged ion on ionic bonds?

  Forms stronger ionic bonds
• What is the relationship between lattice enthalpy and melting point?

  Higher lattice enthalpy equals higher melting point

  
• What are the properties of metal oxides regarding lattice enthalpy and melting points?

  • Very exothermic lattice enthalpies
  • Very high melting points
  • Used as protective coatings in furnaces

  
• What other factors may affect melting point besides lattice enthalpy?

  Packing of ions in an ionic lattice

  
• How does ion size affect hydration enthalpy?

  Smaller ions form stronger ionic bonds

  
• What is the effect of larger ions on ionic bonds?

  Form weaker ionic bonds