15.1 Energy Cycles

• Standard enthalpy change of formation(ΔHf): The enthalpy change when one mole of a compound is formed from its elements under standard conditions
• Enthalpy change of combustion (ΔHc): enthalpy change which occurs when one mole of the compound is burned completely in oxygen under standard conditions
• Born-Haber Cycle is used to find the lattice enthalpy
• Lattic enthalpy: the change in enthalpy that occurs when one mole of a solid compound is seperate into it gaseous form under standard conditions

  MX(s) > M⁺(g) + X⁻(g) ∆Hlat >0
• Enthalpy of atomization: the standard enthalpy change that occurs on the formation of one mole of seperate gaseous atoms of an element in its standard state

  M(s) > M(g) ∆Hat >0

  1/2X2 (g) > X(g) ∆Hat > 0
• Ionization Energy: is the standard enthalpy change that occurs on the removal of 1 mol of electrons from 1 mol of atoms or positively charged ions in the gaseous state. For metal ions with multiple valence electrons there can be multiple ionization energies

  M(g) > M⁺(g) + e⁻ ∆Hie >0
• Electron affinity: is the standard enthalpy change on the addition of 1 mol of electrons to 1 mol of atoms in the gaseous phase

  X(g) + e⁻ > X⁻ ∆Hea <0
• Constructing the Born-Haber cycle

  The born-haber cycle combines the lattic enthalpy, enthalpy of atomization, ionization energy, and the electron affinity to find the enthalpy of formation of an ionic compound

  • The different changes in enthalpy get added together
• Generalized Born-Haber Cycle

  A) ∆Hie

  B) ∆Hat (X)

  C) ∆Hat (M)

  D) ∆Hea (X)

  E) ∆Hlat

  F) ∆Hf

  
• Variation in lattice enthalpy values

  1. An increase in the ionic charge will result in a greater attraction between opposing charge ions increase the lattice enthalpy
  2. A the distance between the bonded ions increases, the strength of the electrostatic attraction decreases, decreasing the lattice enthalpy
• Enthalpy of solution : the change in ethalpy that ocurs when one mole of a solute (ionic compound) is dissolved to form aqueous ions in an infinitely dilute solution under standard conditions

  MX(s) > M⁺(aq) + X⁻(aq) ∆Hsol usually >0
• Enthalpy of hydration: the change in enthalpy that occurs when 1 mole of gaseous ions is dissolved in water to form an infinitely dilute solution of one mole of aqueous ions under standard conditions

  M⁺(g) > M⁺(aq) ∆Hhyd <0

  X⁻(g) > X⁻(aq) ∆Hhyd <0

  • Solvation is used in pae of hydration for solvents other than water
• The lattice enthalpy, enthalpy of hydration, and enthalpy of solution form a cycle