Thermodynamics

• What are Born-Haber cycles similar to?

  Hess’s Law
• What do Born-Haber cycles allow us to determine?

  Enthalpy changes that cannot be measured directly
• What are lattice enthalpies used for?

  Ionic substances
• How is lattice dissociation enthalpy defined?

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

  Energy required to form an ionic lattice from gaseous ions
• What is atomisation enthalpy defined as?

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

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

  They are treated like vectors, reversing the sign if the cycle counters the direction of the arrow
• How is the lattice enthalpy of formation calculated in a Born-Haber cycle?

  By following around the cycle from the start to the head of the arrow
• What is the formula for calculating lattice enthalpy in the example provided?

  ∆H = --355 - 121 - 502 - 107 - 411
• What is the enthalpy of solution defined as?

  Enthalpy change when one mole of ionic solid is dissolved in water to infinite dilution
• What is the enthalpy of hydration defined as?

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

  Water has a ∂+ region that attracts negative ions
• What does the perfect ionic model assume about ions?

  All ions are perfectly spherical and display no covalent character
• What causes covalent character in ions?

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

  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 the overall entropy change for a reaction measured?

  In JK$-1$mol$-1$
• What is true for all spontaneous reactions regarding entropy?

  They 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?

  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