Thermodynamic Notes

THERMODYNAMICS Most of the physical and chemical processes in the nature occur due to energy changes. Energy is a state function of the system, defined as a property which can be converted to work. Thermodynamics is one such study of energy and its transformations. It is defined as a study of inter-relation of various forms of energy systems (may be physical or chemical under a set of conditions constitutes the sub!ect of thermodynamics. This study is of p rime importance as it is used to deduce and elucidate the following aspects of physical chemistry such as" #. $ant %off&s 'aw . )hase rule *. 'aws of chemical e+uilibrium Applications of thermodynamics •

The criteria of the feasibility or spontaneity of chemical reactions under a given set of conditions are eplained by the laws of thermodynamics.

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The study also determines the etent until which eactions can proceed. Limitations of the stdy

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The laws of thermodynamics are applicable to substances of macroscopic aggregation or bulk, but not to the individual atoms or molecules of systems. The reason is due to the atoms being highly unstable and studying the thermodynamics of such molecules become immensely difficult.

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The laws account for the feasibility of a reaction, however fails to predict the rate of the reaction. Important terminolo!ies" System

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 portion of the universe which is chosen for thermodynamic study.

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It consists of a definite amount of specific substances which is surrounded by a well-defined boundary.

 Illstrations" /onsider the case of a piece of ice. The eistence of only ice is a

state function which depends on both pressures () and temperature (T. 0tudying the thermodynamics of the ice becomes the system. Srrondin! •

)art of the universe remaining outside the boundaries of a system which can echange both energy and matter. The system is separated from the surrounding by a boundary. This can be a fied, 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#srrondin!$. 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 epression, 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 epressed in calories per degree or 3oules per degree kelvin. (34-# Types of systems

5pen system  system which can echange both energy and matter.  typical eample 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

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/losed system  closed system is one in which no transfer of matter to and from the surroundings is possible but energy can be echanged across the boundaries with the surroundings. 'i! * A closed systems in +hich there is e)chan!e of ener!y +ith the srrondin!s 7o echange of matter with surroundings 6ater

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Thermally isolated system  system which can echange 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 echange 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 Insulated closed system 7o echange of matter and energy

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Thermodynamic properties of a system

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.rim 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. Eample" 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. Eample 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 #