?G?r (T) = -RTlnK

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?G?r (T) -RTlnK ?G?r (T) ?H?r (T) - ?S?r
(T) How do we evaluate ?H?r (T) ? How do we
evaluate ?S?r (T) ?
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Since both ethylene and cyclobutane are gases at
room temperature and above, all we need is the
heat capacity of the gas phase. How do we
measure the Cp(g)(298) of benzoic acid (solid),
or of methyl salicylate (liquid)?
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Ethylene at 298 K ?Sf (298) Sethylene - 2 Sf
H2 -2 SfC Sethylene(298) 219.5 J mol-1K-1 2 Sf
H2 2(4.184)(31.2) 261.2 J mol-1K-1 2 SfC
2(4.184)(1.361) 11.4 J mol-1K-1 ?Sf (298)
(C2H4) 219.5-261.2-11.4 -53.1 J mol-1K-1
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Cyclobutane at 298 K ?Sf (298) Scyclobutane -
4 Sf H2 - 4 SfC Scyclobutane(298) 265.4 J
mol-1K-1 4 Sf H2 4(4.184)(31.2) 522.4 J
mol-1K-1 2 SfC 2(4.184)(1.361) 22.8 J
mol-1K-1 ?Sf (298) (C4H8) 265.4-522.4-22.8
-279.8 J mol-1K-1
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?Sf (298) (C4H8) -279.8 J mol-1K-1 ?Sf (298)
(C2H4) -53.1 J mol-1K-1 Cyclobutane ? 2
ethylene ?Sr (298) 2(-53.1) - (-279.8) 173.6
J mol-1K-1 ?Sr (298) 2 Sethylene -
Scyclobutane ?Sr (298) 2(219.5) - 265.4 173.6
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?Gf (298) ?Hf (298) - T ?Sf (298) Ethylene
?Hf (298) 52300 ?Sf (298) -53.1 ?Gf
(298) 52300 - (298)(-53.1) 68130 J
mol-1 Cyclobutane ?Hf (298) 28400 ?Sf
(298) -279.8 ?Gf (298) 28400 - (298)(-279.8)
111780 J mol-1 Cyclobutane ? 2 ethylene ?Gr
(298) 2(68.13) - 111.78 24.5 kJ mol-1 ?Gr
(298) 76200 - (298)(173.6) 24.5 kJ mol-1
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Ethylene
Cp(g) 67 J mol-1K-1
Sethylene(773) Sethylene(298) 219.5 J
mol-1K-1 Sethylene(773) Sethylene(298)
Sethylene(773) Sethylene(298) Cp(g)
ln(773/298)
Sethylene(773) 219.5 63.9 283.4 J mol-1 K-1
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Cyclobutane
Cp(g) 135 J mol-1K-1
Scyclobutane (298) 265.4 J mol-1K-1 Scyclobutan
e(773) Scyclobutane(298) Cp(g)ln(773/298) Scy
clobutane(773) 265.4 128.7 394 J mol-1K-1
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?Gf (773) ??Hf (773) - T ?S (773) Ethylene
?Hf (773) 84125 S (773)
-283.4 Cyclobutane ?Hf (773) 92525 S (773)
-394 ?Gf (773) ??Hf (773) - T ?S (773) ?Gf
(773) 2(84125)-92525-T2(-283.4)-(-394) ?Gf
(773) 75700 - (773)(-172.8) -57850 J mol-1