Thermodynamics Flashcards
enthalpy of solution definition
standard enthalpy change when 1 mol of an ionic solid is dissolved in water so the ions don’t interact and are well separated
trend in lattice enthalpy of formation down a group
becomes less negative
what does the perfect ionic model assume
ions are perfectly spherical (electron cloud is not distorted) and bonding has no covalent character (purely electrostatic)
which features result in a tendancy towards covalent character
+ve ion is small
+ve ion has multiple charges
-ve ion is large
-ve ion has multiple charges
how does lattice change when bonding has some covalent character
lattice becomes stronger
why is calcium chloride CaCl2 not CaCl or CaCl3
CaCl2 has the most exothermic enthalpy of formation so is the most thermodynamically stable
what is entropy at 0k
0 as elements do not move
unit of entropy
J/K/mol
change in entropy equation
sum of change in products- sum of change in reactants
what does gibbs free energy represent
the balance between entropy and enthalpy
how faesable a reaction is
what value will gibbs free energy have if change is spontaneous
negative
when would a reaction not occur even if gibbs free energy is negative
if activation energy is very high then the reaction will be so slow it essentially does not occur
gibbs free energy eqn.
∆G= ∆H-T∆S
∆G during phase change
as the reaction is reversible, ∆G will be 0
can therefore calculate mp, bp etc. from this
effect of increase in temperature when ∆S is +ve
more likely the reaction will occur as ∆G is more -ve
effect of temperature when ∆S is close to 0
very small effect as -T∆S will be small so ∆G won’t change much
what does each thing represent when free gibbs eqn. is applied to a straight line graph of temperature against ∆G
gradient is equal to -∆S
y intercept = ∆H
the reaction becomes feasable when the line crosses the x axis
enthalpy of solution equations (2)
∆Hsolution= -∆Hformation + sum of ∆HhydH
∆Hsolution= ∆HL dissociation + sum of ∆H hydH
why are hydration enthalpies exothermic
energy is given out when water molecules bond to metal ions
higher charge density means larger hydration enthalpy
when is a substance more likely to be soluble
if ∆H solution is exothermic
but positive ∆S can make the reaction faesable
