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PHYSICAL CHEMISTRY
THERMODYNAMICS 2 AND PHASE EQUILIBRIA
UNIVERSITY OF NAIROBI
System and state
SYSTEM is the object we are studying at a given moment
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They are usually either constant volume or constant pressure regardless of changes taking place in the
system
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AN OPEN SYSTEM is where there are both exchanges of energy and matter with the surroundings and
therefore can undergo changes in the composition
A CLOSED SYSTEM is the system that can exchange energy but not matter with the surrounding
AN ISOLATED SYSTEM can exchange neither matter nor energy with the surroundings
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II
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Is a flask that is not stopped to which various substances can be added
Biological cell because nutrients and wastes can pass through the cell wall
Human beings can also open cells because we ingest, respire, perspire and
excrete

Example of closed system
A stopped flask where energy can be exchanged within the context of the flask because walls are able
to conduct heat
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The state of the system is the circumstances in which it is found, expressed by numerical values

of a sufficient sets of variables
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II
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Pressure
b
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Temperature

All other macroscopic state variables are dependent variable with values given by a
mathematical functions of the independent variables
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There are different branches of thermodynamics
 Classical thermodynamics under which we discuss equilibrium
or reversible thermodynamics
we also discuss irreversible thermodynamics

 Statistical thermodynamics
Reversible classical thermodynamics
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It deals with matter in bulk and does not consider the behavior of individual
particles
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Thermal energy (dH)
Gibbs-free energy

Classical reversible thermodynamics also seals with equilibrium
conditions and there are two tendencies for the system to get into
equilibrium
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Lowest energy
Maximum randomness

Classical irreversible thermodynamics
 deals with fluxes or movement of matter
statistical thermodynamics
 deals with matter of individual particle and its uses spectroscopic and quantum laws
the difference between classical and statistical thermodynamics is that classical
thermodynamics gets its data from calorimetric can be determined under different
conditions whereas statistical thermodynamics gets its data from spectroscopy
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To engineer thermodynamics helps in:
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calculation of the amount of work that can be derived from a given
specific amount of fuel
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To a manufacturing chemist thermodynamics helps in:
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Establishing the stability of a product
Establishing the maximum yield expected from thermodynamics
calculation
Avoiding undesirable by-products by telling us the optimum
conditions of temperatures and pressure expected
The proper choice of solvent to use for a systematic chemist as well
as an analytic chemist

Limitations of thermodynamics

 it does not tell us when the reaction starts, or how fast the reaction takes place

in case calculations of the thermodynamics indicate the occurrence of the
reaction
 apart from the three types of state discussed above there is also: a diathermic
system where the system permits heating as a mode of transfer of energy
a diabatic -where the system does not permit heating even
though there is a difference in temperatures
exothermic-is a process in a system that heats or releases heat
into the surroundings
endothermic-is a process in the system that is heated by the
surroundings or absorbs heat from the surrounding
state of the system -is a condition of the system when
macroscopic properties have definite measurable values if any
of the macroscopic properties of a system changes such as
temperatures and pressure the state of the system also changes
Isochoric process-Is a constant temperature process

The cyclic process is- one in which the system returns to its
initial state after undergoing a series of changes
Isobaric process-is a constant pressure process

Reversible changes-which is sometimes referred to as quasiequilibrium or quasi-static
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Irreversible changes -this is carried out so rapidly that the
system does not return to its initial state
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e
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Extensive properties are those values that depend on the quality of
matter contained in any system e
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mass, volume, area, energy,
number of moles, enthalpy and entropy
Intensive properties are those which depend on the nation of a
substance and is independent of its amount size in the system e
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