Born-Haber cycles, and lattice energy Mr Michael (Hamzah) Allan (019 254 7120) Mr Michael (Hamzah)...

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Transcript of Born-Haber cycles, and lattice energy Mr Michael (Hamzah) Allan (019 254 7120) Mr Michael (Hamzah)...

  • Slide 1
  • Born-Haber cycles, and lattice energy Mr Michael (Hamzah) Allan (019 254 7120) Mr Michael (Hamzah) Allan (019 254 7120)KYUEM
  • Slide 2
  • 5. Chemical energetics (p23) b) explain and use the term: iii)lattice energy (H negative, i.e. gaseous ions to solid lattice)
  • Slide 3
  • Definition: Lattice energy (enthalpy) is the enthalpy change when one mole of an ionic crystal (lattice) is formed from its constituent gaseous ions under standard conditions...
  • Slide 4
  • Crystal (lattice) forms (Ionic) Bond forming
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  • H LE = -ve H LE = -x kJmol -1 (Ionic) Bond forming
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  • H = +ve H = +x kJmol -1 (Ionic) Bond --breaking-- i.e. H = - LE
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  • Examples (1/4). Na + (g) + Cl - (g) NaCl(s) H LE = -781 kJmol -1 gaseous ions Standard state for the product Remember to state the units sign
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  • Examples (2/4). K + (g) + O 2 - (g) KO 2 (s) H LE = -1540 kJmol -1 gaseous ions Standard state for the product Remember to state the units sign Potassium superoxide
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  • Write a thermochemcial equation for the lattice energy of barium chloride given that the 0.1 moles of the salt formed (in the appropriate manner) liberates 235.2 kJ of energy Answer = Ba 2+ (g) + 2 Cl - (g) BaCl 2 (s) H LE = -2352 kJmol -1 Examples (3/4) D.I.Y.
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  • Examples (4/4) 2K + (g) + O 2 2- (g) K 2 O 2 (s) H LE = -1980 kJmol -1 gaseous ions Standard state for the product Remember to state the units sign Potassium peroxide
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  • Points of significance about Lattice energy
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  • 5. (e) (iv) Born-Haber cycles 5. (e) (iv) Born-Haber cycles (P23) (including ionization energy and electron affinity)
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  • Uses of Lattice energy. Born-Haber cycles, which shows the step-wise process of lattice formation from elements. Born-Haber cycles have numerous uses, e.g. predicting the stability of an ionic compound.
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  • Other definitions to learn (1/3) 1 mole of a compoundformed from its elementsin their standard states Enthalpy of formation ( H f ): 1 mole of a compound is formed from its elements in their standard states under standard conditions. 1 mole of gaseous atomsformed from its element Enthalpy of atomization ( H at ): 1 mole of gaseous atoms is formed from its element under standard conditions.
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  • Other definitions to learn (2/3) 1 mole of electrons removed from 1 mole of gaseous atoms Ionization energy ( H IE ): 1 mole of electrons is removed from 1 mole of gaseous atoms under standard conditions. NOTE: Removing e- from atoms is always an endothermic process. Energy must be supplied to overcome the attraction of the e- to the nucleus. The more e- that are removed, the more endothermic the process will be.
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  • One mole of electronsadded toone mole of gaseous atoms Electron affinity enthalpy ( H ea ): One mole of electrons is added to one mole of gaseous atoms under standard conditions. Note: The first eas are almost always negative. (noble gasses excepted). 2 nd and later eas are ALWAYS positive (adding an electron to an already negative ion = repulsion to overcome) Other definitions to learn (3/3)
  • Slide 20
  • Standard conditions (1/2). To keep all data comparable (therefore easy to use and easily transferable), measurements are usually taken under standard conditions. 1 atmosphere (101 kPa, 760mmHg, 1 barr) 298K (25oC but must use K temperatures in equations) 1 Molar solution (see electrochemistry etc)
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  • Standard conditions (2/2). The symbol H is accompanied with a symbol to donate standard conditions, i.e. H If no symbol is present, assume standard conditions are used, unless stated otherwise (and mention them in definitions, e.g. Standard enthalpy of atomization)
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  • Datum line (zero energy line) Na(s) + Cl 2 (g)