lecture 6 Flashcards
what type of function is entropy
it’s a state function
- current value doesn’t depend on route taken to get there
if a system starts and ends at the same place,, what is its entropy
0
in a reversible reaction at constant temp,, the heat added is:::
minus the work done
U = q + w = 0
in expansion,, what results in an increase in entropy
V > 0
0 > p
Cp of monatomic gas
5nR /2
entropy of fusion is equal to what
enthalpy of fusion / T
- for all phase transitions under equilibrium conditions
S= q/t
but q = H at standard pressure
entropy change of phase change
change S = change H / T
for vaporisation
sublimation
under equilibrium conditions
entropy changes on raising temperature,, what do we do when we heat things + phase transitions occur
total change in S =
H(fus)/T. + Cp ln(T1/To) + H(vap)/T
Cp ln(t1/to) = S when raising temp at a constant pressure.
H/T = S when phase changes are occurring.
we need to add them bc as we go from liquid to solid,, we heat it ( S when increasing temp) then it melts (S when phase change occurs) so we must add them if we want to find the total S from liquid -> gas.
when is Cp constant with Temperature
in liquid water
that’s why we do the H/T + Cp ln(T/T) when finding S for increasing temp and phase changes in liquids
bc Cp is constant with temp
when is Cp not constant with T
low temperatures
solid phase
Cpm equals what at low temperatures near 0k
aT^3
for non metallic solids
entropy, for changes in temp in non metallic solids, near 0k (very low temperatures) is equal to what
change in S = 1/3 Cpm
what is the entropy of anything at 0k ( 0 kelvin,, very low temperatures)
entropy is 0
apart from imperfect crystals( their imperfections add disorder)
how is entropy 0 at 0k
equation: S = k ln (W)
at 0k,, W = 1
so S = 0
when can absolute entropy be found for lower temperatures
if we know the heat capacity at all lower temperatures
