()
∆
G =
∆
H  T
∆
S
()
(+)
Effect of
∆
H and
∆
S
An exothermic rxn that
spreads energy.
Yeah!
It will always be spontaneous (
∆
G <0).
Section 9.7
2Na(s) + 2H
2
O(l)
!
2H
2
(g) + 2NaOH
0 mol gas
!
2 mol gas
Energy Dispersed
∆
S > 0
Gives off heat
∆
H < 0
A fool could get this reaction to work.

()
(+)
∆
G =
∆
H  T
∆
S
(+)
()
An endothermic rxn that
concentrates energy.
This will rxn will never, ever
happen spontaneously (
∆
G >0)
Section 9.7
2H
2
O (l) + O
2
(g)
!
2H
2
O
2
(aq)
1 mol gas
!
0 mol gas
Energy concentrated
∆
S < 0
Requires heat
∆
H > 0
Effect of
∆
H and
∆
S
Laugh at the fool that tries to get this to work spontaneously.

(+)
∆
G =
∆
H  T
∆
S
()
()
An exothermic rxn that
concentrates energy.
As long is the temperature is low,
(T
∆
S smaller than
∆
H) it will happen spontaneously.
Section 9.7
H
2
O(l)
!
H
2
O(s)
liquid
!
solid
Energy concentrates
∆
S
o
< 0
Gives off heat
∆
H
o
< 0
S
L
G
S
L
G
H
Effect of
∆
H and
∆
S

(+)
News flash:
Stuff freezes when it’s cold.
∆
G =
∆
H  T
∆
S
(+)
(+)
An endothermic rxn that
spreads energy.
As long is the temperature is high
(T
∆
S larger than
∆
H) it will happen
Section 9.7
H
2
O(l)
!
H
2
O(g)
0 mol gas
!
1 mol gas
Energy Dispersed
∆
S > 0
Requires heat
∆
H > 0
S
L
G
S
L
G
H
Effect of
∆
H and
∆
S

()
News flash:
Stuff evaporates when it’s hot.
Reaction Spontaneity Summary
∆
H
∆
S
Spontaneous (
∆
G < 0)

+
always
+

never
+
+
at high T, when T
∆
S > 
∆
H


at low T, when 
∆
H > T
∆
S
Section 9.7 Summary
∆
G =
∆
H  T
∆
S
At low temp,
∆
G is the same sign as
∆
H
At high temp,
∆
G is the opposite sign of
∆
S,
unless
∆
S~0, in which case,
∆
G is the same sign as
∆
H
Free Energy (
∆
G)
temperature
∆
G < 0 rxn spontaneous
∆
G > 0 rxn nonspon
∆
H>0
∆
H>0,
∆
S>0
rxn works at hi temp
+
+
slope = T
∆
S
(
∆
S > 0)
∆
H<0
∆
H<0,
∆
S>0
rxn works every time

+
slope = T
∆
S
(
∆
S < 0)
∆
H<0,
∆
S<0
rxn works at lo temp


∆
H>0,
∆
S<0
rxn never works
+

Section 9.8
Free Energy, Enthalpy and Entropy
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