8: Born Haber Cycles and Enthalpies of Solution Flashcards
Enthalpy Definitions Born Haber Cycles Enthalpy of Solution Perfect Ionic Model
Define enthalpy change.
The heat energy transferred in a reaction at constant pressure.
Why do exothermic reactions have a negative enthalpy change?
Heat energy is released to the environment.
Why do endothermic reactions have a positive enthalpy change?
Heat energy is absorbed into the reaction.
What is lattice enthalpy?
The energy required to break a bond between two ions. They essentially measure ionic bond strength.
How do you measure lattice enthalpy?
Using Born-Haber cycles. They cannot be measured directly.
Define enthalpy change of formation. Give an example using Ca and Cl2
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states.
Ca(s) + Cl2 (g) -> CaCl2(s)
Define bond dissociation enthalpy. Give an example using Cl2.
The enthalpy change when all of the bonds of the same type in 1 mole of gaseous molecules are broken.
Cl2(g) -> 2Cl(g)
Define enthalpy of atomisation of an element. Give an example using Cl2.
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard states.
0.5Cl2(g)->Cl(g)
Define enthalpy change of atomisation of a compound. Give an example using NaCl.
The enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms.
NaCl(s) - Na(g) + Cl(g)
Define first ionisation energy.
The enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms.
Define second ionisation energy.
The enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions.
Define first electron affinity.
The enthalpy change when 1 mole of gaseous 1- ions is made from 1 mole of gaseous atoms.
Define second electron affinity.
The enthalpy change when 1 mole of gaseous 2- ions is made from 1 mole of gaseous 1- ions.
Define the enthalpy change of hydration. Use the example of Na+
The enthalpy change when 1 mole of aqueous ions is formed from gaseous ions.
Na+ (g) -> Na+(aq)
Define enthalpy change of solution
The enthalpy change when 1 mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution.
