Thermodynamics

• What is the enthalpy of atomisation of an element?


  Enthalpy change for 1 mole of gaseous atoms
• What is the enthalpy change for sodium atomisation?

  +148 kJ mol-1
• What is the enthalpy change for oxygen atomisation?

  +249 kJ mol-1
• 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
• What is the bond dissociation enthalpy for Cl2?

  +242 kJ mol-1
• How is the bond dissociation enthalpy related to atomisation enthalpy for diatomic molecules?

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

  Energy to remove 1 mole of electrons
• What is the second ionisation enthalpy?

  Energy to remove electrons from 1+ ions
• What is the first electron affinity?

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

  • 141.1 kJ mol-1
• Why is the first electron affinity exothermic for certain atoms?

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

  +798 kJ mol-1
• 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 enthalpy of lattice dissociation?

  Energy change when ionic lattice separates
• What is the enthalpy of hydration for Li+?

  • 519 kJ mol-1
• What is the enthalpy of hydration for F-?

  • 506 kJ mol-1
• Why is the enthalpy of hydration always exothermic?

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

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

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

  • 411.2 kJ mol-1
• What is the Born-Haber cycle used for?

  • To calculate lattice enthalpy indirectly
  • Links various enthalpy changes together
  • Applies Hess's law
• How is the lattice enthalpy calculated using the Born-Haber cycle?

  By rearranging the enthalpy changes
• What is the lattice enthalpy for NaCl?

  • 787 kJ mol-1
• 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 result in 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
  • Attractions are purely electrostatic
  • Used for calculating theoretical lattice enthalpies
• What happens when ionic substances have covalent character?

  Theoretical and experimental values differ
• What is the relationship between theoretical and Born-Haber lattice enthalpies?

  • Born-Haber is the experimental value
  • Theoretical assumes perfect ionic character
  • Differences indicate covalent character
• Why does calcium chloride have the formula CaCl2?

  Most exothermic enthalpy of formation
• What is the driving force behind spontaneous reactions?

  Exothermic reactions lead to stability
• What is entropy?

  Measure of disorder in a system
• How does the arrangement of atoms affect entropy?

  More arrangements lead to higher entropy
• Which state of matter has the lowest entropy?

  Solid
• Which state of matter has the highest entropy?

  Gas
• How does temperature affect entropy?

  Higher temperature increases entropy
• What does an exothermic reaction produce in terms of thermodynamic stability?

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

  Exothermic reactions leading to stability