thermodynamics Flashcards
What does Hess’ law state
the enthalpy change of a reaction is independent of the route taken
define standard enthalpy of formation
the enthalpy change when one mole of a compound is formed from its constituent elements in standard conditions, with all products and reactants in their standard states
what is the standard enthalpy of an element
0
define standard enthalpy of combustion
the enthalpy change when one mole of a substance is completely burnt in excess oxygen
define standard enthalpy of atomisation
enthalpy change when one mole of gaseous atoms is formed from a compound in its standard state in standard conditions
define first ionisation energy
enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions
define second ionisation energy
enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
define first electron affinity
enthalpy change when one mole of gaseous atoms gain one mole of electrons to form one mole of gaseous 1- ions
define second electron affinity
enthalpy change when one mole of gaseous 1- ions gains one mole of electrons to form one mole of gaseous 2- ions.
define lattice enthalpy of formation
enthalpy change when one mole of solid ionic lattice is formed from its constituent gaseous ions.
define lattice enthalpy of dissociation
enthalpy change when one mole of solid ionic lattice is dissociated into its gaseous ions
define enthalpy of hydration
enthalpy change when one mole of gaseous ions become hydrated/dissolved in water to infinite dilution
define enthalpy of solution
enthalpy change when one mole of solute dissolves completely in a solvent to infinite dilution.
define mean bond dissociation enthalpy
enthalpy change when one mole of covalent bonds is broken, with all species in the gaseous state
what is a born haber cycle
thermochemical cycle showing all the enthalpy changes involved in the formation of an ionic compound. start with elements in their standard state.
what factors affect the lattice enthalpy of an ionic compound
size of the ion
charge of the ion
how can you increase the lattice enthalpy
smaller ion
charge centres will be closer together increasing the charge. increased electrostatic forces of attraction.
how can born haber cycles be used to see if compounds could theoretically exists
use known data to predict certain values and then see if these compounds would be thermodynamically stable.
what happens when a solid is dissolved in terms of interactions of the ions with water
break lattice
gaseous ion, dissolve
surrounded by water
what is the perfect ionic model
perfectly spherical
even charge distribution
no covalent character
what kind of bonds will be the most ionic
between large positive ions and small negative ions
define spontaneous and feasible
it will take place of its own accord
is a reaction with a positive or negative enthalpy change more likely to be spontaneous
negative
define entropy
randomness of a system
units of entropy
JK-1mol-1
what is the second law of thermodynamics
entropy always increases, as it is overwhelmingly more likely for molecules to be disordered than ordered
is a reaction with positive or negative entropy change more likely to be spontaneous
positive
compare the general entropy for solids, liquids and gases
solids < liquids < gases
how do you calculate the entropy change for a reaction
sum of products entropy - sum of reactants entropy
gibbs free energy
delta G = delta H - Tdelta S
what does gibbs free energy show
if delta G < / = 0 then the reaction is feasible
why is entropy 0 at 0K
no disorder
