Topic 13- Further energetics Flashcards
what does Hess’ law state?
the enthalpy change of a reaction is independent of the route taken
what is standard enthalpy of atomisation?
The enthalpy change when one mole of gaseous atoms is formed from a compound in its standard state in standard conditions
define first ionisation energy
The 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
The 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
The enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous 1- ions
define second electron affinity
The 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
The enthalpy change when one mole of solid ionic lattice is formed from its constituent gaseous ions
define enthalpy of hydration
The enthalpy change when one mole of gaseous ions becomes hydrated/dissolved in water to infinite dilution (water molecules totally surround the ion)
define enthalpy of solution
The enthalpy change when one mole of a solute dissolves completely in a solvent to infinite dilution
define mean bond dissociation enthalpy
The enthalpy change when one mole of ( a certain type of) covalent bonds is broken, with all species in the gaseous state
what factors affect the lattice energy of an ionic compound?
- size of ions
- charge of ions
how can you increase the lattice enthalpy of a compound? why does this increase it?
- smaller ions, since the charge centres will be closer together
- increased charge, since there will be a greater electrostatic force of attraction between the oppositely charged ions
- increasing the charge of the anion has a much smaller effect than increasing the charge on the cation, since increasing anion charge also has the effect of increasing ionic size
How can Born-Haber cycles be used to see if compounds could theoretically exist?
use known data to predict certain values of theoretical compounds, and then see if these compounds would be thermodynamically stable. (was used to predict the existence of the first noble gas containing compound)
what actually happens when a solid is dissolved in terms of interactions of the ions with water molecules?
- break lattice —> gaseous ions, dissolve each gaseous ion in water.
- the aqueous ions are surrounded by water molecules *which has a permanent dipole due to O-H polar bond)
what is the perfect ionic model?
- assumes that the ions are perfectly spherical
- even charge distribution (100% polar bonds)
why is the perfect ionic model often not accurate?
- ions aren’t perfectly spherical
- polarisation often occurs when small cations or large anions are involved (so the ionic bond gain covalent character)
- some lattices are not regular and the crystal structure can differ
which kind of bonds will be the most ionic? why?
between large positive ions and small negative ions e.g. CsF
define the terms spontaneous and feasible
if a reaction is spontaneous and feasible, it will take place on its own accord, does not take into account rate of reaction
what is a spontaneous process?
a spontaneous process is one that takes place without continuous intervention from us
is a reaction with a positive or negative enthalpy change more likely to be feasible?
negative (exothermic)
what is entropy?
entropy is a measure of the dispersal of energy in a system which is greater when the system is more disordered
what is the symbol of entropy?
S
which is more disordered- solid or gas?
gas
what is the unit of standard entropy?
J K-1 mol-1
