1.08 thermodynamics

• define enthalpy of formation.

  Enthalpy change when 1 mole of a compound is formed from its elements with all substances in their standard states.
• define enthalpy of combustion.

  the enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in their standard states.
• define enthalpy of neutralisation.

  Enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions.
• define ionisation energy.

  The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
• define electron affinity.

  the enthalpy change when one mole of gaseous atoms gain one mole of electrons to form one mole of gaseous 1- ions.
• define enthalpy of atomisation.

  enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.
• define hydration enthalpy.

  The enthalpy change when one mole of gaseous atoms are hydrated. (dissolved in water)
• define enthalpy of solution.

  enthalpy change one mole of an ionic solid dissolved in enough water so that the dissolved ions are well seperated and do not interact.
• define bond dissociation enthalpy.

  The energy required to break one mole of covalent bonds in a gaseous state.
• define lattice enthalpy of formation.

  enthalpy change when one mole of solid ionic compound is formed from its constituent ions in a gaseous state.
• define lattice enthalpy of dissociation.

  enthalpy change when one mole of a solid compound is broken up into its constituent ions in gaseous states.
• define enthalpy of vaporisation.


  Enthalpy change when one mole of a liquid is turned into a gas.
• define enthalpy of fusion.

  Enthalpy change when one mole of a solid is turned into a liquid.
• what does endothermic mean?

  energy is required / enthalpy number is positive.
• what does exothermic mean?

  releases energy / enthalpy change is negative.
• define enthalpy change.

  The heat energy transferred in a reaction at constant pressure.
• what are standard conditions?

  100kPa and 298K
• is the enthalpy of formation endo or exo?

  can be either.
• is the enthalpy of ionisation endo or exothermic?

  endothermic.
• what is the enthalpy of formation for elements?

  zero.
• why is the second ionisation more endothermic?

  it required more energy to remove an electron from a cation than a neutral atom as their attraction between the nuclei and outermost electron is stronger.
• is enthalpy of atomisation exo or endothermic?

  endothermic.
• is bond enthalpy endo or exothermic?

  endothermic.
• is lattice enthalpy of formation endo or exothermic?

  exothermic.
• why is lattice enthalpy of formation so exothermic?

  because ionic compounds are much more stable than the gaseous ions due to strong electrostatic forces of attraction between the oppositely charged ions.
• is electron affinity exo or endothermic?

  the first one is always exothermic.

  
  

  the second one can be both.
• why is second electron affinity more endothermic than the first?

  large forces of repulsion must be overcome requiring lots of energy.
• in born haber cycles do endothermic reactions go up or down?

  up.
• in born haber cycles do exothermic reactions go up or down?

  down.
• What must be assumed when calculating theoretical lattice enthalpies?

  The bonds have a perfect ionic model.
• What a does a perfect ionic model consist of?

  Ions that are perfectly spherical with the charge evenly distributed throughout.
• What factors are to blame for the difference between theoretical and experimental lattice enthalpies?

  The ionic compounds experience covalent character, changing the size and charge of the ions.
• What does covalent character mean?

  Positive ions distort the charge distribution in the negative ion, polarising it and causing it to change shape.
• What is the difference between a more covalent and less covalent character?

  More covalent means more polarised therefore more shape change.
• What is entropy?

  A measure of disorder in a system. In any physical and chemical changes, processes move from order to disorder and entropy increases
• How does covalent character change lattice enthalpy?

  Lattice enthalpy will be larger than expected as it requires more energy to break / form
• What are the factors affecting entropy

  Physical state, dissolving, number of particles
• What is the critical temperature

  Where the reaction just becomes feasible