Thermodynamics

• What is the definition of enthalpy change of formation?

  Enthalpy change when one mole of compound formed from constituent elements with all reactants + products in standard states under standard conditions
• What is the definition of lattice enthalpy of formation?

  Enthalpy change when one mole of solid ionic compound formed from its gaseous ions
• What is the lattice enthalpy of dissociation?

  Enthalpy change when one mole of solid ionic compound broken up into gaseous ions
• What is the bond dissociation enthalpy?

  Enthalpy change when one mole of covalent bonds is broken in the gaseous state
• What is the enthalpy change of first ionisation energy?

  Enthalpy change needed to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous +1 ions
• What is the enthalpy change of atomisation?

  Enthalpy change when one mole of gaseous atoms formed from an element in its standard state
• What is the second ionisation energy?

  Enthalpy change needed to remove one mole of electrons from one mole of +1 gaseous ions to form one mole of gaseous +2 ions
• What is the first electron affinity?

  Enthalpy change needed to gain one mole of electrons by one mole of gaseous atoms to form one mole of gaseous -1 ions
• What is the second electron affinity?

  Enthalpy change needed to gain one mole of electrons by one mole of gaseous -1 ions to form one mole of gaseous -2 ions
• What is the enthalpy change sign for exothermic reactions?

  Negative enthalpy change
• What is the enthalpy change sign for endothermic reactions?

  Positive enthalpy change
• What happens to the energy sign when moving against the arrow in the Born-Haber cycle?

  The sign of the energy changes
• What is the relationship between the enthalpy change and the route taken in a Born-Haber cycle?


  It is independent of the route taken
• What does a negative lattice enthalpy indicate?

  It indicates an exothermic reaction
• How do you check if your lattice enthalpy calculation is correct?

  Ensure total value adds up to zero
• What is the significance of the lattice enthalpy of formation of lithium chloride?

  It shows the energy released when forming solid
• What does a positive lattice enthalpy value indicate?

  It indicates an endothermic reaction
• What is the enthalpy change of solution?

  Energy change when one mole of an ionic solid dissolves in sufficient water to form an infinitely dilute solution
• What is the difference between theoretical and experimental lattice enthalpies?

  Theoretical assumes perfect ionic model
• What causes the difference between theoretical and experimental lattice enthalpies?


  Covalent character in ionic compounds
• What happens to the charge distribution in a distorted ion?

  It becomes unevenly distributed
• What is the effect of polarisation on ionic compounds?

  It increases covalent character
• Why is the second electron affinity of oxygen endothermic?

  Due to repulsion between negative charges
• How does the size of the ion affect lattice enthalpy?

  Larger ions lead to greater distortion
• What happens to ionic compounds when they dissolve in water?

  They break apart into ions and hydrate
• What is required for an ionic compound to dissolve?

  Bonds must break and new bonds form
• Why is the process of breaking ionic bonds endothermic?

  It requires heat energy to break bonds
• What type of solvents do most ionic compounds dissolve in?

  Polar solvents
• What is the enthalpy of hydration?

  Enthalpy change when one mole of gaseous ions become hydrated to form aqueous ions
• What happens to the energy during the hydration of ions?

  Energy is released during hydration
• What is entropy in chemistry?

  Measure of disorder in a system
• How does increasing disorder affect entropy?

  Higher disorder leads to higher entropy
• What happens to the entropy when more moles of gas are produced?

  Entropy increases
• What is the formula for calculating entropy change?

  ΔS = S(products) - S(reactants)
• In what units is entropy measured?

  Joules per Kelvin per mole (J/K/mol)
• What is the relationship between the order of solids, liquids, and gases?

  Gases>liquids>solids
• Why is the reaction entropically favorable?

  Because entropy allows the reaction to occur
• What are the standard conditions for measuring entropy?


  1 mole, 100 kPa, 298 K
• What is the equation for Gibbs free energy?

  ΔG = ΔH - TΔS
• What does a negative ΔG indicate?

  The reaction is feasible