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more practically... in a
CHEMICAL REACTION
A
<---> B
Which Way will it go?
ΔG
= ΔG0’
+ R T ln [p]/[r]
Gibbs studied
the change in free energy of a reaction as a
function of temperature,
... deriving a variation of the
equation indicating free energy depends upon:
1. energy is stored in molecule's covalent bonds
2. but
remember, temperature is negligible in cells which
are isothermal, thus,
ΔG
= actual free
energy at any time during a reaction's progress
ΔGo' = standard free
energy [change under standard
conditions: 23oC (296 K),
1 atmosphere,
reactants @ 1 [M], & pH 7.0]
R
= gas
constant (1.987 x 10-3 Kc/mol)
T
= absolute
temp (273oK), thus @ 23oC = 296oK
ln
= natural
log (for conversion to log10
multiply by 2.303)
but, at equilibrium
ΔG =
0 and we can call the [p]/[r] =
Keq (Equilibrium Constant)
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if we solve above equation for ΔGo' we can see the relationship
of Keq
to ΔGo’
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Free Energy Equation...
ΔG =
ΔG0’
+ RT
ln [P]
[R]
@ equilibrium ΔG
= 0 .... thus rearranging
ΔG0’
= - RT ln [P]_
[R]
@ equilibrium, we define that the
[P] is = to the
Keq Equilibrium constant
[R]
@ 230C ...
-RT ln Keq =
-(2.0) (296) (2.303) lg10 Keq
= -
[1364] lg10 Keq
thus under standard cellular conditions...
ΔG0’
= -
[1364] lg10 Keq
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