THE SPONTANEITY AND EQUILIBRIUM
MK. Kesetimbangan Kimia FMIPA UNS
Fitria Rahmawat
Fundamental concepts
• Kind of matters:
– Substances
– Mixture of substances Kind of Substances:
– elements: can not be broken into smaller substance by ordinary chemical method
– Compounds: can be broken into smaller substance by ordinary chemical method
– *ordinary chemical method: involving energy 1000
kJ/mol.
• Concept of atomic and molar mass
• The formulas
• The mole
• Chemical equations
– A shorthand method for describing chemical transformation
– Mn0 2 + 4HCl ---4 MnCl2 + 2H20 + Cl2
– The balance of chemical equation is an expression of law of conservation of the mass
– stoichiometri
Kinds of energy
The fundamental equation of thermodynamics
• The mechanical properties: p and V
• The three fundamental properties: U, S and T
• The three composite properties: H, G and A
• For present discussion: the expansion work,
The composite functions:
The Helmholtz free energy is a thermodynamic potential that measures the useful" work obtainable from a closed
thermodynamic system at a constant temperature and volume.
The negative of the difference in the Helmholtz energy is equal to maximum amount of work that the system can perform in a thermodynamic
process in which volume is held constant.
Hermann Ludwig Ferdinand von Helmholtz August 31, 1821
Differentaton:
The propertes of A
The propertes of G
• The objects of Thermodynamics is to seek out logically the
relation between kinds of energy and their diverse manifestation.
• The laws of thermodynamics govern the transformation of
one kind of energy into another.
• THE FIRST LAW OF THERMODYNAMICS IS THE LAW OF ENERGY CONSERVATION
the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed
• THE SECOND LAW OF THERMODYNAMICS: IS
CONCERN WITH THE DIRECTION OF NATURAL
PROCESS.
• THE ZEROTH LAW OF THERMPDYNAMICS: SYSTEMS IN
THERMAL EQUILIBRIUM WITH EACH OTHER HAVE THE
SAME TEMPERATURE
For ideal gas
Entropy and the third law of thermodynamics
The entropy of a perfect crystal, at absolute zero (zero kelvins ), is exactly equal to zero
THE SPONTANEITY AND EQUILIBRIUM
• Aim is to find out what characteristics distinguished the irreversible (real)
transformation to reversible (ideal) transformations.
• What relation between entropy changes with
the heat flow that accompany it
It’s the Clasius Inequality
Transformaton at constant temperature (isothermal)
It is known that:
TdS = dU + dW
For isothermal change : TdS = d(TS)
the work produced in an is othermal transf ormation is less than or equal to the decrease in the Helmholtz energy
Transformation at constant temperature and under constant pressure
And , TdS = d(TS)
or
Therefore under constant temperature and constant pressure:
G is called the free energy of the System.
At equilibrium:
the decrease in Gibbs energy associated with a change in state at constant T and p is equal to the maximum work
Wa, rev which is obtainable in the transf ormation
Spontaneous changes can continue to occur in such a system as long as the Gibbs energy of the system can decrease, that is, until the Gibbs energy o f the system reaches a minimum value, which is dG = 0
the algebraic sign tells us whether
a transf ormation can occur in the direction in which we imagine it.
There are three possibilities :
The word "spontaneous" applied to changes in state in a thermo dynamic sense must not be given too bro ad a meaning
.It means only that the change in state is possible
What can be done about those transf ormations that have G po sitive and are thermo dynamically impossible, or
nonspontaneous ?
Human nature being what it is, it does not submit lightly to the jud gment that a certain change is "impossible ." The
"impossible “ flow of water uphill can be made "p ossible,"
