Thermodynamics

• enthalpy change = Heat (energy) change at constant pressure
• electron affinity = enthalpy change for one mole of gaseous atoms to be converted to one mole of 1- ions
• atomisation = enthalpy change forming one mole of gaseous atoms from elements in their standard states
• ionisation energy = enthalpy change for one mole of gaseous atoms to be converted into one mole of 1+ ions
• lattice enthalpy of formation = enthalpy change for one mole of a solid ionic lattice to form from its gaseous ions
• solution = enthalpy change when one mole of solute is dissolved in enough solution to make an infinitely dilute solution
• hydration = enthalpy change when one mole of aqueous ions are formed from gaseous ions
• To form bonds, the particles must give out energy (a negative enthalpy change) meaning it is exothermic
• Ca2+ has a less negative enthalpy change of hydration than Mg2+ because it is a larger ion so has a larger distance between the outer shells and the nucleus. This means it has weaker attractions from the nucleus so has a weaker attraction to the Oδ- in water.
• In an exothermic reaction (negative ΔH), increasing the temperature will shift the equilibrium to the left so more reactants formed. In an endothermic reaction (positive ΔH), increasing the temperature will shift the equilibrium to the right so more products are formed.
• Second electron affinity usually requires energy because you are adding an electron to an already negative ion.
• Second ionisation energy is greater than the first because it is harder to remove an electron from a positive ion than a neutral atom. This is because there is decreased shielding.
• Larger ions have weaker electrostatic forces of attraction than smaller ions. This means less energy is required to separate larger ions, making the enthalpy of lattice dissociate less endothermic (require less energy).
• A higher temperature is used when change ΔH and ΔS are positive to increase the rate of reaction.
• Enthanlpy of solution triangle:

  A) enthalpy of solution

  B) enthalpy of lattice formation

  C) enthalpy of hydration

  D) lattice

  E) gas

  F) solution

  
• When enthalpy of solution is negative (exothermic reaction) an increase in temperature will shift the equilibrium to the left producing more reactants to oppose the change. Hence solubility will decrease.
• Change in enthalpy (ΔH) = change is energy of products - change in energy of reactants
• Change in entropy (ΔS) = change in entropy of products - change in entropy of reactants
• Free energy (ΔG) = change in enthalpy (ΔH) - (temperature (K) x change in entropy (ΔS))
• If free energy (ΔG) is less than 0 then a reaction is feasible. When both ΔH and ΔS are positive or both negative a reaction is dependent on the magnitude of the values. If ΔH is negative and ΔS is positive then ΔG will always be negative and therefore the reaction is always feasible. If ΔH is positive and ΔS is negative then ΔG will always be positive and the reaction will never be feasible.
• Feasibility

  A) positive

  B) negaitve

  C) positive

  D) negaitve

  E) sometimes feasible

  F) never feasible

  G) always feasible

  H) sometimes feasible

  I) ΔS

  J) ΔH

  
• The lower the difference in electronegativity of a lattice, the more the degree of covalency which means the enthalpy of lattice formation is lower.