THERMODYNAMICS
THERMODYNAMICS
Most of the physical and chemical processes in
Most of the physical and chemical processes in the nature occur due to energythe nature occur due to energy changes. Energy is a state function of the system, defined as
changes. Energy is a state function of the system, defined as a property whicha property which can be converted to work. Thermodynamics is one such study of energy and can be converted to work. Thermodynamics is one such study of energy and itsits transformations. It is defined as a study of inter-relation of various forms of transformations. It is defined as a study of inter-relation of various forms of energy systems (may be physical or chemical under a
energy systems (may be physical or chemical under a set of conditionsset of conditions constitutes the sub!ect of thermodynamics. This study is of p
constitutes the sub!ect of thermodynamics. This study is of p rime importancerime importance as it is
as it is used to deduce and elucidate the following aspects of physicalused to deduce and elucidate the following aspects of physical chemistry such as"
chemistry such as" #.
#. $ant %off&s 'aw$ant %off&s 'aw .
. )hase rule)hase rule *.
*. 'aws of chemical e+uilibrium'aws of chemical e+uilibrium Applications of thermodynamics Applications of thermodynamics
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• The criteria of the feasibility or spontaneity of chemical reactions underThe criteria of the feasibility or spontaneity of chemical reactions under
a given set of conditions are eplained by
a given set of conditions are eplained by the laws of thermodynamics.the laws of thermodynamics.
•
• The study also determines the etent until whichThe study also determines the etent until which
eactions can proceed. eactions can proceed. Limitations of the stdy Limitations of the stdy
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• The laws of thermodynamics are applicable to substances ofThe laws of thermodynamics are applicable to substances of
macroscopic aggregation or bulk, but not to the individual atoms or macroscopic aggregation or bulk, but not to the individual atoms or molecules of systems. The reason is due to the atoms being highly molecules of systems. The reason is due to the atoms being highly unstable and studying the thermodynamics of such molecules become unstable and studying the thermodynamics of such molecules become immensely difficult.
immensely difficult.
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• The laws account for the feasibility of a reaction, however fails to predictThe laws account for the feasibility of a reaction, however fails to predict
the rate of the reaction. the rate of the reaction. Important terminolo!ies" Important terminolo!ies" System
System
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• portion of the universe which is portion of the universe which is chosen for thermodynamic study.chosen for thermodynamic study. •
• It consists of a definite amount of specific substances which It consists of a definite amount of specific substances which isis
surrounded by a
Illstrations"/onsider the case of a piece of ice. The eistence of only ice is a state function which depends on both pressures () and temperature (T. 0tudying the thermodynamics of the ice becomes the system.
Srrondin!
• )art of the universe remaining outside the boundaries of a system which
can echange both energy and matter. The system is separated from the surrounding by a boundary. This can be a fied, movable real or
imaginary. Entropy
• Is a +uantitative term deciding the feasibility of a reaction. It refers to
the randomness or the disorderness of a system. It is denoted by 0. The total entropy is given by S#total$%ΔS(system)&ΔS#srrondin!$. If a process is
carried out in a thermodynamically reversible manner, so that d+ i s the amount of heat absorbed by the system at constant temperature, then the entropy change, ds, of the system id given by the epression,
ds1 d+2dt
If 0 is the entropy of the final state and 0# is the entropy of the initial
state of a system under investigation, the increase in the entropy Δs, is given by the e+uation,
Δs10-0#1 ʆ d+2dt
Entropy is epressed in calories per degree or 3oules per degree kelvin. (34-#
Types of systems 5pen system
system which can echange both energy and matter. typical eample can be water present in an open container. The water here represents the system. s the container is open, more water can be added and hence the thermodynamics of such a system can be monitored efficiently.
'i! ( An e)chan!e of matter and ener!y in an open system
$apour
6ater %eat
/losed system
closed system is one in which no transfer of matter to and from the surroundings is possible but energy can be echanged across the boundaries with the surroundings.
'i! * A closed systems in +hich there is e)chan!e of ener!y +ith the srrondin!s
Thermally isolated system
system which can echange neither energy nor matter with i ts
surrounding is called an isolated system. definite amount of water sealed or enclosed in a container which is thermally insulated. The system does not echange heat or matter with the surrounding and retains the same state and thermodynamic properties.
'i! , No e)chan!e of ener!y and matter in an isolated system
Thermodynamic properties of a system
7o echange of matter with surroundings 6ater %eat Insulated closed system 7o echange of matter and energy
The characteristic physical properties such as pressure, temperature, volume, mass, density, internal energy, enthalpy, etc, are known as thermodynamic properties which defines the state of the system. 0ince the state of the system changes with the change in any of the properties are called as state variables. It follows that when a system changes from one state to another, there is invariably a change in one or more of the thermodynamic properties. Thermodynamic e-ili.rim of a state
The state of a system in which the macroscopic properties do not undergo any change with time is said to be in thermodynamic e+uilibrium.
Eample" Ice in a refrigerator, a substance in a vacuum flask. Types of processes in thermodynamics
#. Isothermal process
process is said to be isothermal if the temperature of the system remains unaltered during each stage of the process.
. Iso.aric process
process is said to be isobaric if the pressure of the system remains unaltered during each step of the process.
*. Adia.atic process
process is said to be adiabatic if no heat enters or leaves the system during each step of the process.
8. Isochoric process
process is said to be isochoric if there is no change in volume of the system during each stage of the process.
'irst La+ of thermodynamics
This law is a version of law of conservation of energy for
thermodynamic systems. The law states that the total energy of an isolated system is constant and can be transformed from one form to another but cannot be created or destroyed.
Eample for the first law
6hen an engine burns fuel, it converts the energy in the fuels chemical bonds into useful mechanical work and then to heat. 9ifferent fuels
have different energy, but in any given gallon or litre of fuel, there is a set amount of energy.
The conversion of energy principle defined by the first law says that when all the fuels energy is released by burning the engines cylinder, it doesn:t disappear. The total +uantity of energy stays same and is
accounted for. ;or every #<< units of fuel energy that is burned, #<< units of converted energy has to end up somewhere. It doesn:t
disappear.
Applications of first la+ In an open system
• Can predict ho+ mch the pressre drop is across the no//le or ho+
mch ener!y is re-ired .y the pmp to pmp flid0
• amont of heat transfer in the heat e)chan!er • Amont of +or1 prodced .y the tr.ine200
In a closed system
A piston cylinder arran!ement
cylinder has some gas in it. ssume there is no air leakage to the
surrounding. 0o it is a closed system. ssume gas is absorbing some heat =, also assume that the gas is able to push the piston upwards due to high pressure of the gas. This enables the gas to perform work.
Therefore>ΔE1=-6 de2dt1=-6
6
ΔE =
