thermodynamics is the branch of physics which deals with the study of transformation of heat energy into other form and vice versa
One of the most important concept of thermodynamics is the temperature for example
We are cautious about hot foods hot stoves.
Agricultural engineers are concerned with weather conditions for the health of crops
Doctors are concerned about their present temperature for further investigation
food engineers are concerned with proper heating and proper cooling of item of food.
Geologist are concerned with the transfer of thermal energy and so on.
an assembly of an extremely large number of particles of atom or molecules is called thermodynamics system.such a system may exist in the form of a solid liquid or gas or a combination of two or more States.
thermodynamics system is said to be in thermodynamic equilibrium when macroscopic variables like pressure volume temperature mass composition etc that characterize the system do not change with time.
for example a gas enclosed in a rigid container an insulated completely from its surrounding it in a state of thermodynamic equilibrium.
An isolated system is always in thermal equilibrium.
Zeroth law was formulated by R.H. Fowler only in 1931 ,much later than the first and the second laws of thermodynamics
according to Zeroth law when the thermodynamics system A and b are separately in thermal equilibrium with a thermodynamic system c then the system A and b are in thermal equilibrium with each other also.
the physical quantity that determines whether or not given system a is in thermal equilibrium with another system b is called temperature.
obviously to system are in thermal equilibrium the temperature must be same and if they are not in thermal equilibrium the temperature must be different.
Heat is the energy that flows from higher temperature to lower temperature. This floor is only because of different in temperature.
internal energy of a system is the total energy possessed by the system due to molecular motion and molecular configuration. It is represented by U.
The Energy due to molecular motion is called internal kinetic energy energy.
The energy e due to molecular configuration is called internal potential energy.
internal energy of a real gas is the sum of internal kinetic energy and internal potential energy of the molecules of a gas. It would obviously depend on both the temperature and the volume of gas.
the following points regarding internal energy should be clearly understood
internal energy of a system is a microscopic state variable of the system. the internal energy of a given mass of gas depends on its state described by a specified values of pressure volume and temperature.
Internal energy of a system does depend on state of system but not on how that state was achieved or not on history of achieving the state that is not on the path taken to arrive at that state.
In thermodynamics the kinetic energy of the system as of whole is not developed it means if the container of a gas is moving as a whole with some velocity the kinetic energy of the container is not to be included in internal energy.
the internal energy of a real gas can be changed by changing any of the macroscopic state variables of the gas.
tour ways of changing the state and hence internal energy of a gas are
heating the cylinder containing the gas or keeping the cylinder in contact with the body at higher temperature. Some heat flows from hotter body to the gas on account of temperature difference. therefore internal energy of the gas increases.
using the piston of the cylinder containing gas in the opposite direction some work is done by the gas due to which the internal energy of a gas decreases.
note that both these things could happen in the reverse direction to for example if the gas we are in contact with a body at lower temperature from heat wood floors from gas to the surrounding resulting in fall in temperature and hence decrease in its internal energy similarly if the piston we are used downwards work will be done on the gas therefore internal energy of the gas would increase.
thermodynamic state variable of a system are the parameters which describe equilibrium state of the system for example aquarium state of a gas is completely specified by the values of pressure volume temperature mass and composition if there is a mixture of gas. the various state variables of a system are not necessarily independent.
the equation of state represent the connection between the state variable of a system for example the equation of state of an ideal or perfect gas is represented as PV is equal to nrt.
Thermodynamic state variables are of two type
Extensive state variable and intensive state variable.
example imagine a gases system in thermal equilibrium divided into two equal parts. The state variables ,volume , mass and internal energy which gets half in each part or extensive variables.the other state variables like pressure, temperature and density which remain unchanged for each part are Intensive in variables.
Quasi static process.
a process aura change in the state variables of a thermodynamic system which is infinitely slow is call quasi-static process
in a static process the difference in the pressure of the system and the external pressure is infinitely small similarly the difference between the temperature of the system and the temperature of the Sun and surrounding is infinitesimally small therefore quadristatic process must be infinitely slow.
Thermodynamic processes
thermodynamics process is said to be take place when some change occur in the state of a thermodynamic process that is thermodynamic parameter of the system change with time.
Following are some of the important thermodynamic process
Isothermal process is that which occur at constant temperature.
adiabatic process is that in which no heat intas aur lips thermodynamics system during the change.
Isochoric process is that which occurs at constant pressure.
Isochoric or isovolumic process is that which occurs at constant volume.
Indicator diagram
the indicator diagram for PV diagram represents the variation of volume of a system with the pressure of the system.
Isothermal operation or change
a change in pressure and volume of a gas without any change in its temperature is called an isothermal change. in such a change there is a free exchange of heat between the gas and its surroundings.
Hence the two essential conditions for a perfect isothermal change are
the wall of the container must be perfectly conducting to allow free exchange of heat between the gas and its surrounding.
the process of compression for expansion should be slow so as to provide time for exchange of heat between the gas and its surroundings.
Perfect isothermal changes are practically impossible.
Some example of isothermal change are.
melting process is an isothermal change because temperature of a substance remain constant during melting.
Similarly boiling process is also an isothermal operation.
as ine also thermal operations temperature is kept constant pressure and volume are related to each other by Boyle's law that is PV is equal to constant aur P1V1 is equal to P2 V2.
for an ideal gas in isothermal process there is no change in internal energy of the gas that is DU is equal to zero this is because t is equal to constant that is d t is equal to zero.
Adiabatic operation aur change
a change in pressure and volume of a gas when no heat is allowed to enter or escape from the gas is called an adiabatic change. obviously temperature of the gas will also change in adiabatic operation.
obviously for an adiabatic change the exchange of heat between the gas and the surrounding must be prevented hence the two essential condition for a perfect adiabatic change are.
the wall of the container mostly perfectly non conducting in order to prevent any exchange of heat between the gas and and its surrounding and
the process of compression expansion should be certain so that there is no time for exchange of heat
Perfect adiabatic change are practically impossible
Some example of nearly perfect adiabatic change are
sudden compression expansion of a gas in a container with perfectly non conducting wall.
Sudden busting of the tube of a bicycle tyre.
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