Thermodynamics

• What are Born-Haber cycles used for?


  To determine enthalpy changes that cannot be measured directly
• What are lattice enthalpies used for?


  They are used for ionic substances
• What is lattice dissociation enthalpy?


  The energy required to break apart an ionic lattice into gaseous ions
• How is lattice formation enthalpy defined?


  It is the energy required to form an ionic lattice from gaseous ions
• What is atomisation enthalpy?


  The energy required for the formation of a mole of gaseous atoms
• What does the enthalpy of electron affinity represent?


  The enthalpy change when one mole of electrons is added to gaseous atoms
• How is the lattice enthalpy of formation calculated in a Born-Haber cycle?


  By following the cycle from the start of the arrow to the head
• What is the enthalpy of solution?


  The enthalpy change when one mole of ionic solid is dissolved in water
• How is the enthalpy of hydration defined?


  It is the enthalpy change when one mole of gaseous ions is dissolved in water
• Why is the enthalpy of hydration usually negative?


  Because water attracts negative ions due to its partial positive region
• What assumptions does the perfect ionic model make?

  • All ions are perfectly spherical
  • Ions display no covalent character
• What is entropy a measure of?


  It is a measure of disorder in a system
• How does temperature affect entropy?


  Entropy increases as temperature increases
• Which state of matter has the greatest entropy?


  Gases
• What happens to entropy when a substance melts or evaporates?


  There is a sudden increase in entropy
• How is overall entropy change for a reaction measured?


  It is measured in JK$-1$mol$-1$
• What is the relationship between spontaneous reactions and entropy?


  All spontaneous reactions have a positive entropy value
• What does Gibbs Free-Energy (∆G) allow us to find?


  It allows ∆S to be found without measuring effects on surroundings
• What is the equation used to determine Gibbs Free-Energy?


  ∆G = ∆H - T∆S

  
• In what units is free-energy measured?


  Free-energy is measured in kJmol$-1$
• What does a negative ∆G indicate?


  It indicates that the reaction is spontaneous
• How does temperature affect the feasibility of a reaction?


  Changing the temperature can change the feasibility of the reaction