Thermodynamics

• What is the enthalpy of atomisation of an element?

  Enthalpy change for 1 mole of gaseous atoms
• How is the enthalpy of sublimation related to the enthalpy of atomisation?

  They are numerically the same for solids
• What is the bond dissociation enthalpy?

  Enthalpy change when a covalent bond breaks
• How is the bond dissociation enthalpy related to the enthalpy of atomisation for diatomic molecules?

  It equals 2 times the enthalpy of atomisation
• What is the first ionisation enthalpy?

  Energy to remove 1 mole of electrons
• What is the reaction for the first ionisation enthalpy of magnesium?

  Mg (g) → Mg+ (g) + e-
• What is the second ionisation enthalpy?

  Energy to remove 1 mole of electrons from 1+ ions
• What is the reaction for the second ionisation enthalpy of magnesium?

  Mg+ (g) → Mg2+ (g) + e-
• What is the first electron affinity?

  Energy change when atoms gain electrons
• What is the reaction for the first electron affinity of oxygen?

  O (g) + e- → O- (g)
• Why is the first electron affinity exothermic for certain atoms?

  Ion is more stable than the atom
• Why is the second electron affinity endothermic for oxygen?

  Energy is needed to overcome repulsion
• What is the enthalpy of lattice formation?

  Energy change when ionic lattice forms
• What is the reaction for the enthalpy of lattice formation of NaCl?

  Na+(g) + Cl- (g) → NaCl (s)
• What is the enthalpy of lattice dissociation?

  Energy change when ionic lattice separates
• What is the reaction for the enthalpy of lattice dissociation of NaCl?

  NaCl (s) → Na+(g) + Cl- (g)
• Why do lattice formation and dissociation have opposite signs?

  Formation releases energy, dissociation absorbs energy
• What is the enthalpy of hydration?

  Energy change when gaseous ions become aqueous
• Why is the enthalpy of hydration always exothermic?

  Bonds form between ions and water molecules
• What is the enthalpy of solution?

  Energy change when ionic solid dissolves in water
• What is the enthalpy change of formation?

  Energy change when 1 mole of compound forms
• What is the reaction for the enthalpy change of formation of NaCl?

  Na(s) + ½Cl2 (g) → NaCl (s)
• What is the Born-Haber cycle used for?

  To calculate lattice enthalpy indirectly
• How does Hess's law relate to the Born-Haber cycle?

  Heat of formation equals the sum of changes
• What is the formula for calculating lattice enthalpy using Hess's law?

  ΔLattH = ΔfH - (sum of other changes)
• What factors affect the strength of lattice enthalpy?

  Sizes and charges of the ions
• How does the size of ions affect lattice enthalpy?

  Larger ions lead to weaker lattice enthalpy
• How does the charge of ions affect lattice enthalpy?

  Higher charges lead to stronger lattice enthalpy
• What is the perfect ionic model?

  Assumes ions are 100% ionic and spherical
• What happens when ionic substances have covalent character?

  They exhibit distortion in charge clouds
• How do theoretical and Born-Haber lattice enthalpies differ?

  Born-Haber values are experimental and real
• Why does calcium chloride have the formula CaCl2?

  Most stable form with exothermic formation
• What is the relationship between ionisation energy and lattice enthalpy?

  Higher ionisation energy leads to stronger lattice
• What is entropy?

  Measure of disorder in a system
• How does temperature affect entropy?

  Higher temperature increases disorder and entropy
• How do solids, liquids, and gases compare in terms of entropy?

  Gases have the highest entropy, solids the lowest
• How do elements compare to compounds in terms of entropy?

  Elements generally have lower entropy than compounds
• What does an exothermic reaction result in regarding product stability?

  Products are more thermodynamically stable
• What is a driving force behind spontaneous reactions?

  Exothermic reactions leading to stable products
• Can endothermic reactions be spontaneous? How?

  Yes, due to entropy considerations