Thermodynamics

• What is the definition of enthalpy of formation?

  One mole of substance formed from elements
• Under what conditions is the enthalpy of formation defined?

  All substances in their standard state
• What is the definition of enthalpy of combustion?

  One mole of substance undergoes complete combustion
• What is produced during the enthalpy of combustion process?

  Complete combustion in oxygen
• What is the definition of enthalpy of neutralisation?

  One mole of water is formed from acid and alkali
• What is the result of the enthalpy of neutralisation reaction?

  Water formed under standard conditions
• What is the definition of first ionisation enthalpy?

  Enthalpy change when one mole of gaseous atoms loses one electron
• What does the first ionisation enthalpy produce?

  One mole of gaseous +1 ions
• What is the definition of second ionisation enthalpy?

  Enthalpy change when +1 ions lose one electron
• What does the second ionisation enthalpy produce?

  One mole of gaseous +2 ions
• What is the definition of first electron affinity?

  Each atom gains one electron to form -1 ions
• What is an example of first electron affinity?

  O(g) + e- --> O-(g)
• What is the definition of second electron affinity?

  Each ion gains one electron to form -2 ions
• What does the second electron affinity produce?

  One mole of gaseous -2 ions
• What is the definition of atomisation enthalpy?

  One mole of gaseous atoms from an element
• What is an example of atomisation enthalpy?

  1/2 I2 (s) --> I (g)
• What is the definition of hydration enthalpy?

  One mole of gaseous ions become hydrated
• What is an example of hydration enthalpy?

  Mg2+ (g) + aq --> Mg2+ (aq)
• What is the definition of enthalpy of solution?

  One mole of ionic solid dissolves in water
• What is an example of enthalpy of solution?

  MgCl2 (s) + aq --> Mg2+ (aq) + 2Cl (aq)
• What is the definition of bond dissociation enthalpy?

  One mole of covalent bonds broken in gaseous state
• What is an example of bond dissociation enthalpy?

  I2 --> 2I
• What is the definition of lattice enthalpy of formation?

  One mole of solid ionic compound from gaseous ions
• What is the definition of lattice enthalpy of dissociation?

  One mole of solid ionic compound broken into gaseous ions
• What is the definition of enthalpy of vaporisation?

  One mole of liquid turned into a gas
• What is the definition of enthalpy of fusion?

  One mole of solid turned into a liquid
• Second electron affinity is...

  Endothermic
• What does it mean if there is a larger discrepancy between the perfect ionic model and the theoretical model?

  The model has more covalent character.
• Explain the difference between perfect ionic and theoretical in ZnSe.

  • Zn2+ is small with a highly positive charge
  • Se2- is large with a high negative charge
  • Se2- is easy to distort as it is large and electrons are far from nucleus
  • Electrons are shared -> covalent
• What factors increase covalent character?

  • small size and highly positively charged positive ion
  • large size and highly negatively charged negative ion
  • more sharing
• What is entropy?


  Entropy is a measure of the disorder or randomness in a system.
• What is the order of highest entropy?

  Gas > Liquid > Solid
• How do we calculate entropy change?

  entropy of products - entropy of reactants
• What does it mean if the gibbs free energy change is negative?

  The reaction is feasible
• What are the units for entropy?

  J K^-1 mol^-1
• What do we equate to 0 when working out what temperature a reaction becomes feasible at?

  G
• What is the formula for Gibbs free energy change?

  delta g = delta h - t x delta s
• Why may a reaction not occur, even if it is feasible?

  • There is a large activation energy barrier
  • System is kinetically inert or stable
• What factors affect lattice enthalpy?

  • ion size
  • charge
• Why do we have a higher enthalpy of hydration with higher charge?

  • Greater attraction to water molecules
  • More exothermic reaction
  • More stable ion