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Forward toward equilibrium:
Reverse toward equilibrium:
At equilibrium: ΔG = 0; Q = K
Escaping equilibrium:1) Coupled reactionsΔGcoupled < 0 drives reaction
2) Doing work on systemElectrochemistry, enzymes
First law
Second law
Reaction at constant pressure
Reaction at constant pressure
Working with ΔG
Calculate from tabular data
ΔG changes with concentration
⇒
⇒
(calculate ΔG from Q vs K)
ΔG and non-PV work
closedsystem⇒
(electrochemistry)
heat out
work on
work by
heat in
Things mix, expand, break down
Temperatures even out
Reactions reach equilibrium
Direction of chemical reaction
surrounding
(calculate ΔG° from K)
Glossary
G: Gibbs energy = H - TSwnPV: non-PV workH: Enthalpy …°: standardS: Entropy Δ…: change inR: Gas constant …f: of formation
1) Among other things, an ideal fuel for the control thrusters of a
space vehicle should decompose in a spontaneous exothermic
reaction when exposed to the appropriate catalyst. Evaluate the
following substances under standard state conditions as
suitable candidates for fuels.
2) Calculate ΔG° for each of the following reactions from the
equilibrium constant at the temperature given.
3) In glycolysis, the reaction of glucose (Glu) to form glucose-
6-phosphate (G6P) requires ATP to be present as described
by the following equation:
Glu + ATP ⟶ G6P + ADP ΔG º = −17 kJ/mol In this process, ATP becomes ADP summarized by the
following equation:
ATP ⟶ ADP ΔGº =−30 kJ/mol Determine the standard free energy change for the following
reaction, and explain why ATP is necessary to drive this
process:
Glu ⟶ G6P ΔGº = ?
4) What happens to ΔG (becomes more negative or more
positive) for the following chemical reactions when the
concentration (partial pressure) of oxygen is increased?
a. S(s)+O2(g)⟶SO2(g)
b. 2SO2(g)+O2(g)⟶SO3(g)
c. HgO(s)⟶Hg(l)+O2(g)
5) Starting from tabulated enthalpies and entropies of
formation, calculate ΔG° and the equilibrium constant K for
the ammonia synthesis from the elements at temperatures of
100 K, 300 K and 500 K.
6) What is the Gibbs free energy necessary to transport a
hydrogen ion from a solution of pH = 4 to a solution of
pH = 7? Did you expect a positive or a negative value
7) What is the Gibbs free energy for the hydrolysis of ATP
under physiological conditions. The concentration of ATP is
about 5 mM, and that of the products ADP and phosphate is
about 0.5 mM. (See Q3 for the standard Gibbs energy)
8) What is the equilibrium constant for the reaction inside a
1.5 V alkaline battery? In the reaction, two electrons are
transferred (z = 2).