Thermodynamics Flashcards
Hess law
Enthalpy change from reactant to product is the same no matter what route is taken
Enthalpy change
Heat change at constant pressure
Mean bond enthalpy
Energy required to brake one mole of compound into its gaseous atoms averaged over a range of different compounds
Enthalpy of formation
Amount of energy required to form one mole of compound into its elements with all reactants and products in thier standard state
Enthalpy of combustion
Energy required to completely combust one mole of fuel in excess oxygen with reactants and products in their standard states
Enthalpy of atomisation
Amount of energy required to form one mole of gaseous atoms from an element in standard states
Bond enthalpy linked to atomisation
BE is 2x atomisation
First ionisation energy
Energy required to remove one mole of electrons of one mole of gaseous atoms to form one mole of gaseous ions with a single 1+ charge
Second ionisation energy
Energy required to remove from one mole if electrons from one mole of gaseous 1+ gaseous ions to form one mole of 2+ gaseous ions
First electron affinity
Enthalpy change required to convert one mole of gaseous atoms into one mole of gaseous ions with a single negative charge under standard conditions
Second electron affinity
Enthalpy change required to convert one mole of gaseous ions with a single 1- charge into one mole of gaseous ions with a 2- negative charge under standard conditions
Lattice formation enthalpy
Enthalpy change one more or solid ionic compound is formed from its gaseous ions
Lattice dissociation enthalpy
Enthalpy change when one mole of solid ionic compound is formed from its gaseous ions
Enthalpy of hydration
Enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions
Enthalpy of solution
Enthalpy cage when one mole of solute dissolves to form a solution where the ions are far apart to not interact with each other
Why if F2 more electronegative ?
F2 is a smaller molecule which means attracts pair of electrons to nucleus more more than any other diatomic molecule
Comparing strength of IONIC LATTICES
Use CRAM to compare the different ion eg mgcl2 and BaCl2, u compare mg2+ and Ba+ lattice of formation
C=compare charges ( higher charges will have a stronger attraction to the opposite ions) mg2+ has a greater charge
R=Compare radius ( look at shielding ) mg has less shielding so smaller radius so will greater attraction
A=attraction. Therefore mg2+ has a greater attraction to Cl- ion
M= more exothermic if lattice of formation or more endothermic if lattice of dissociation. Mgcl2 has a greater EXOTHERMIC LATTICES OF FORMATION ENTHALPY (have to say theses words )
2 types of techniques for measuring ionic bind strength
- Theoretical
- Experimental
Theoretical
perfect ionic model which has no covelant character, therefore predicts the bonds to be weaker, they have perfect point charges / spheres and so are purely ionic. (SMALLER VALUE)
Experimental
born haber cycle which takes into account covelant character as ions are Polarisable so has a greater value
Order of steps in born harber cycle
- Enthalpy of formation
- Enthalpy of atomisation
- Enthalpy of atomisation (2 times if 2 off )
- First ionisation energy
- Second ionisation energy
- First electron affinity ( 2 times if 2 off )
- Second electron affinity
- Enthalpy of formation of arrow goes down or enthalpy of dissociation if arrow goes up
Calculation lattice enthalpy of solution
Lattice enthalpy of solution = lattice enthalpy ( always positive ) + 2(hydration)
Why is the first electron affinity exothermic
Positive attraction between nucleus and extra electron
What does delta H mean
Standards conditions
