ENTHALPY AND ENTROPY Flashcards
Lattice enthalpy of formation definition
enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions
Enthalpy change of 1st ionisation
enthalpy when 1 mole of gaseous 1+ ions are made from 1 mole of gaseous atoms
How does the size of ions affect strength of ionic bond
the smaller the ionic radii, the stronger the electrostatic attraction between ions as they can pack together much closer so melting and boiling points are much higher
THE HIGHER THE CHARGE DENSITY THE STRONGER THE ELECTROSTATIC ATTRACTION
Enthalpy change of solution definition
When 1 mole of an ionic substance is dissolved in the minimum amount of solvent to ensure no further enthalpy change is observed upon further dilution
Enthalpy change of hydration
the enthalpy change when 1 mole of aqueous ions is made from 1 mole of gaseous ions
How to work out enthalpy change of solution
Lattice dissociation enthalpy + enthalpy change of hydration
2 things that affect the enthalpy change of hydration
the larger the charge the more exothermic, the smaller the ion the more exothermic
What is entropy
the measure of disorder of a system
the number of ways energy can be shared out between particles
How does the number of particles affect entropy
more particles means a higher entropy as there are more ways that energy can be distributed
How can a reaction be feasible
if the changes in entropy overcome the changes in enthalpy
as increasing entropy is energetically favourable
How would an equation show that a reaction is entropically favourable
a higher amount of moles on one side means that direction is favourable as there are more particles, so more ways energy can be distributed
also creating liquids or gases from solids is entropically favourable
a positive entropy entropy value is favourable
Entropy change formula
AND UNITS
Entropy change = entropy of products - entropy of reactants
Joules per Kelvin per mole
Standard conditions of enthalpy
1 mole of substance
298 K
100 kPa
Gibbs free energy formula and what does it show
and what are units
Shows whether a reaction is feasible or not
^G = ^H - T^S
^G = enthalpy change(J/mol) - Temperature(K) x Entropy change(J/K/mole)
units are J/mol
if ^G is negative or 0 then a reaction is feasible
