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
• How is lattice dissociation enthalpy defined?


  As the energy required to break apart an ionic lattice into its constituent ions in a gaseous state
• What is lattice formation enthalpy?


  It is the energy required to form an ionic lattice from its constituent ions in a gaseous state
• What is atomisation enthalpy (∆atH)?


  It is the energy required for the formation of a mole of gaseous atoms under standard conditions
• What does the enthalpy of electron affinity (∆eaH) represent?


  It represents the enthalpy change when one mole of electrons is added to a mole of gaseous atoms
• How are different enthalpy changes combined in a Born-Haber cycle?


  • They are combined similarly to Hess’s Law
  • Arrows represent reactions and are treated like vectors
  • If the cycle counters the direction of the arrow, the sign of the enthalpy change is reversed
• How is ∆leH of formation calculated in a Born-Haber cycle?


  By following around the cycle from the beginning of the arrow to the head of the arrow
• What is the formula for calculating ∆H in the example provided?


  ∆H = --355 - 121 - 502 - 107 - 411
• What is the enthalpy of solution (∆solH)?


  It is the enthalpy change when one mole of ionic solid is dissolved in water to infinite dilution
• What is the enthalpy of hydration (∆hydH)?


  It is the enthalpy change when one mole of gaseous ions is dissolved in water to form one mole of aqueous ions
• Why is the enthalpy of hydration nearly always negative?


  Because water has a ∂+ region that naturally attracts negative ions
• What assumptions does the perfect ionic model make?

  • All ions are perfectly spherical
  • Ions display no covalent character
• What is covalent character in ions?


  It occurs when two joined ions have varying sizes or charges, leading to uneven charge distribution
• What does entropy (∆S) measure in chemistry?


  It measures the disorder of a system
• How does temperature affect entropy?


  Entropy increases as temperature increases because particles gain energy and move further apart
• 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 true about all spontaneous reactions regarding entropy?


  They have a positive entropy value, indicating disorder increases
• What does Gibbs Free-Energy (∆G) allow us to find?


  It allows ∆S to be found without needing to measure the effects on the surroundings
• What factors are used to determine a value for ∆G?


  Reaction temperature, enthalpy (∆H), and entropy (∆S) changes
• In what units is free-energy measured?


  kJmol$-1$
• How can the relationship between ∆G and ∆S be represented graphically?


  As a straight line graph of ∆G against ∆S
• What does a negative ∆G indicate about a reaction?


  It indicates that the reaction is spontaneous
• What happens to the feasibility of a reaction if temperature or type of reaction changes?


  It changes the feasibility of the reaction happening