1.8 - Thermodynamics

• What is the enthalpy of atomisation of an element?

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

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

  +249 kJ mol-1
• How is the enthalpy of sublimation related to the enthalpy of atomisation?

  They are numerically the same
• 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
• What is the bond dissociation enthalpy for methane (CH4)?

  +435 kJ mol-1
• How is the bond dissociation enthalpy related to the enthalpy of atomisation for diatomic molecules?

  It is twice the enthalpy of atomisation
• What is the first ionisation enthalpy?

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

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

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

  O (g) + e- → O- (g)
• What is the first electron affinity of 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?

  Energy change when 1- ions gain electrons
• What is the equation for the second electron affinity of oxygen?

  O- (g) + e- → O2- (g)
• What is the second electron affinity of oxygen?

  +798 kJ mol-1
• Why is the second electron affinity endothermic for oxygen?

  Energy overcomes repulsive forces
• What is the enthalpy of lattice formation?

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

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

  -787 kJ mol-1
• What is the enthalpy of lattice dissociation?

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

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

  +787 kJ mol-1
• Why is the enthalpy of hydration always negative?

  Energy is released when bonds form
• What is the enthalpy of hydration for Li+?

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

  -506 kJ mol-1
• What is the enthalpy of solution?

  Energy change when ionic solid dissolves
• What is the equation for the enthalpy of solution of NaCl?

  NaCl (s) + aq → Na+(aq) + Cl-(aq)
• What is the standard enthalpy change of formation?

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

  Na(s) + ½Cl2(g) → NaCl(s)
• What is the standard 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 enthalpy changes for available data
  • Applies Hess's law for thermodynamic calculations
• How is the lattice enthalpy calculated using the Born-Haber cycle?

  By rearranging the enthalpy change equation
• What is the lattice enthalpy for NaCl calculated using the Born-Haber cycle?

  -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?

  Greater charge leads to stronger lattice enthalpy