Gibbs Free energy is one measure of the energy
that is available (measured at constant
temperature and pressure) to transform one
chemical compound to another, or one phase to
another (liquid to solid ...) or to perform a
chemical reaction. When you write a general
process of transformation:
A --- > B
if you perform the transformation at constant
temperature and pressure, and if the product B has
a smaller free energy than the reactant A, the
transformation can proceed on its own (spontaneously).
The Gibbs Free Energy is a quantity that
represents the preferred energy state of a
reaction. The relative Gibbs Free Energies of two
states determines how much of each there will be,
and if one has a lower G.F.E. than the other, it
will be more common.
Thus, for instance, the
carbon dioxide in a can of soda has two possible
states that it can be in: in solution (dissolved),
or as a gas (bubbles).
Under the pressure
inside the can, the conditions favor the carbon
dioxide being in solution. When you open the can,
the GFE is much lower for the carbon dioxide to be
a gas, so it fizzes out as bubbles. Gas is
continually being dissolved back into the soda
just as gas is coming out as bubbles, even in a
glass of water. The higher the GFE of dissolved
gas relative to that of gas, the lower will be the
rate at which gas dissolves and the faster the
rate of which gas will form bubbles.
In college chemistry I learned that Gibbs Free
Energy is the same as Free Energy, and we should
call it Gibbs Free Energy in the U.S. because
Gibbs was an American. Gibbs Free Energy is a
number that tells whether a chemical reaction or
process will occur and how stable the product(s)
will be, based on 2 other thermodynamic properties
- entropy and enthalpy - and temperature.
Spontaneity appears to refer to whether the
reaction will occur or not. Some (most??)
reactions spontaneously go in one direction but
not the other.
Here is a web site you can check
Gibbs Free Energy of Reaction: Predicting
Spontaneity:How Its Done. Predicting the
Spontaneity of a Reaction can be a tricky
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