1.7 Thermodynamics Flashcards
What does a negative ΔH show?
Exothermic Reaction
What does positive ΔH show?
Endothermic Reaction
Define lattice formation enthalpy
The enthalpy change when one mole of a solid ionic compound is formed from it gaseous ions.
Define lattice dissociation enthalpy
The enthalpy change when one mole of a solid ionic compound is completely dissolved into its gaseous ions.
What is special about lattice enthalpy
It cant be measured directly and so a number of different enthalpies have to be combined
Enthalpy change of formation. Symbol and definition.
ΔHf
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states
Bond dissociation enthalpy. Symbol and definition
ΔHdiss
The enthalpy change when all the bonds of the same type in 1 moles of gaseous molecules are broken
Enthalpy change of atomisation of an element. Symbol and definition
ΔHat
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state
Enthalpy change of atomisation of a compound. Symbol and definition
ΔHat
The enthalpy change when 1 mole of a compound in its standard state is converted into gaseous atoms
First ionisation energy
The enthalpy change when 1 mole of gaseous atoms are converted into 1 mole of gaseous 1+ ions
First electron affinity
The enthalpy change when 1 mole of gaseous 1- ions are formed from one mole of gaseous atoms
Enthalpy change of hydration
The enthalpy change when 1 mole of aqueous ions is formed from gaseous ions
Enthalpy of solution
The enthalpy change when 1 mole of an ionic substance dissolves in enough solvent to produce an infinitely dilute solution
How do you measure lattice enthalpy?
Born-Haber cycle
What is Hess’s law?
The total enthalpy change of a reaction is the same no matter which route is taken
What is the Born-Haber cycle equation?
Lattic Enthalpy = -Electron affinity -ionisation energy -atomisation energies + enthalpy of formation
What do you do if you go the wrong way against an arrow in a born haber cycle?
Add a minus sign to the value
How do you calculate enthalpy change of solution?
Lattice dissociation enthalpy + Enthalpy of hydration
What is entropy?
A measure of dissorder
Do substance like order or disorder?
Disorder
What factors effect entropy and why/how?
Physical state - Solids have less entropy than gases as they are fixed to a point
Dissolution - Dissolving a solid increases its entropy
Number of particles - More particles means more entropy
Equation for entropy
ΔS = S(products) - S(reactants)
What must the entropy change be for most reactions to be feasible
Positive
What is ΔG
Free energy change, a measure of how feasible a reaction is
What does a negative or zero ΔG show?
The reaction is feasible
Free energy change equation
ΔG = ΔH - TΔS
