PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Thermodynamics is the branch of physics that deals with the relationships between heat and other forms of energy. In particular, it describes how thermal energy is converted to and from other forms of energy and how it affects matter.

thermodynamics

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Thermodynamics system

An assemble particles whose state can be expressed in terms of pressure, volume and temperature, is called thermodynamic system.

Thermodynamic system is classified into the following three systems

(i) Open System It exchange both energy and matter with surrounding. (ii) Closed System It exchanges only energy (not matter) with surroundings.

(iii) Isolated System It exchanges neither energy nor matter with the surrounding.

Thermal equilibrium

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Two systems are said to be in thermal equilibrium with each other, if they are at the same temperature.

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Zeroth Law of Thermodynamic

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Zeroth law of thermodynamics states that when two systems are in thermal equilibrium through a third system separately then they are in thermal equilibrium with each other also.�

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Thermodynamic state variables

Thermodynamic state variables are the macroscopic quantities which determine the thermodynamic equilibrium state of a system.

These macroscopic quantities are known as thermodynamics state variables.

Since these macroscopic quantities describe the behavior of thermodynamic system it is known as thermodynamic.

As they determine the state of the system that is pressure, volume and temperature, at one particular time they are known as thermodynamic state variables.

Pressures (P), Volume (V), Temperature (T), Mass (m) & Internal energy (U) are the thermodynamic state variables. 

These variables can tell us the position or the condition of any gas at that particular time. 

A system not in equilibrium cannot be described by state variables. It means the macroscopic variables are changing with time and they are not constant.

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PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Que. Out of the following parameters, which parameter doesn’t characterize the thermodynamic state of matter?

a)Temperature

b)Volume

c)Work

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Ans. Work

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Thermodynamic processes:-�1.Isothermal process- A thermodynamic process that takes place at constant pressure is called isothermal process.�

2.Isobaric process:- A thermodynamic process that takes place at constant pressure is called isobaric process.�

3. Isochoric process:- A Thermodynamic process that takes place at constant volume is called isochoric process.�

4.Adiabatic process:- A thermodynamic process in which no heat enters or leaves the system is called adiabatic process.�

5.Cyclic process:- A thermodynamic process in which the system returns to its original state is called a cyclic process.�

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

• Energy that is transferred between a system and its surroundings whenever there is a temperature difference between a system and its surroundings is called Heat.
• Work is said to be done if a body or a system moves through a certain distance in the direction of the applied force . It is given as:
• dW=PdV
• Where P is the pressure of the gas in the cylinder.
• If we consider a bulk system consisting of a large number of molecules, then internal energy; of the system is sum of kinetic energies and potential energies of this molecules.

These energy is possessed by a system due to its molecular system and molecular configuration. The internal energy is denoted by U.

Heat , Work and internal energy

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

First law of thermodynamics

The First Law of Thermodynamics states that heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy. This means that heat energy cannot be created or destroyed. It can, however, be transferred from one location to another and converted to and from other forms of energy. 

A way of expressing the first law of thermodynamics is that any is given by the sum of the heat (Q) that flows across its boundaries and the work (W) done on the system by the surroundings:

ΔU=Q−W

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Que.2 what is the relation between heat, energy, work done and change in internal energy?

a) dQ =dU-dW

b) dW=dQ+dU

c) dQ=dU+dW

d) dW+dQ+du=constant

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Ans. dQ = dU + dW

Expression for the relationship between Cp and Cv

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Que. 15 moles of oxygen is heated at constant volume from 30⁰C to 75⁰C .Calculate the amount of heat required .Given that specific heat of oxygen at constant pressure , Cp= 8 cal per mole per ⁰ C and R=8.31 J per mole k.

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Ans. 4063.5 cal��{hint : Cp –CV =R}

P-V DIAGRAM

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The graph representing the variation of pressure with variation of volume is called P-V diagram . The work done by the thermodynamic system is equal to the area under P-V diagram.

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Second law of thermodynamic

There are 2 statements of second law of thermodynamics given by two scientists:

Kelvin-Planck Statement: - No process is possible whose result is the absorption of heat from a reservoir and the complete conversion of the heat into work.

Clausius statement: - No process is possible whose result is the transfer of heat from a colder object to a hotter object.

Explanation of Kelvin-Planck Statement: It is always impossible that the total amount of heat which is supplied to system will get converted to work, and there will always be loss of heat. Complete conversion of heat into work is not possible.

Explanation of Clausius statement: - Transfer of heat from colder body to hotter body won’t take place until some external work is done on the system.

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

REVERSIBLE PROCESS

Reversible Process

A thermodynamic process is reversible if the process can be turned back such that the system and surroundings return to their original states, with no other change anywhere else in the universe.

This means in the Reversible processes if a process starts from initial state then it goes to final state and then it can reversed back from final state to initial state.

Examples:- Isothermal expansion and compression,  Electrolysis 

A process is reversible if :-

It is quasi-static,

No dissipative forces (that is no loss of heat by friction etc.).

Both initial and final states of the system are in thermodynamic equilibrium with each other.

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

IRREVERSIBLE PROCESS

Irreversible processes are those that cannot be reversed.

Two causes which give rise to irreversible processes.

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1) Irreversible processes takes place at a very fast rate.

2) Dissipative Effects.

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Examples:-Plastic deformation, Combustion, Diffusion, Falling of water from hill.

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Carnot engine

Carnot engine

A Carnot engine is named after Carnot scientist.

It is a reversible heat engine operating between two temperatures.

It has a maximum efficiency which no other engine can have.

Cycle of processes in a Carnot engine

Basic Function of any heat engine is it will take heat Q₁ from a hot reservoir at temperature T₁ and give heat Q₂   to a cold reservoir at temperature T₂.

As system is absorbing heat so it is isothermal expansion. Engine absorbs heat Q₁ at temperature T₁.

An adiabatic process takes place inside the engine because of which there is increase in the temperature of the engine from T₁ to T₂ but no flow of heat.

As system is releasing heat so it is isothermal contraction. Engine releases heat Q₂ at temperature T₂.

An adiabatic process takes place again which changes the temperature of the system from T₂ to T₁.

One cycle of Carnot engine will have Isothermal expansion then adiabatic process, and then isothermal contraction followed by adiabatic process.

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Carnot cycle

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A Carnot cycle is defined as an ideal reversible closed thermodynamic cycle in which there are four successive operations involved and they are isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression. During these operations, the expansion and compression of substance can be done up to desired point and back to initial state.�

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Work done in Isothermal process

�In an isothermal process temperature remains constant.�

Consider pressure and volume of ideal gas changes from (P₁, V₁) to (P₂, V₂).

At any intermediate stage with pressure P and volume change from V to V+ΔV ( ΔV small)�then from first law of thermodynamics�ΔW=PΔV �

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Now taking ΔV approaching zero i.e. ΔV→0  and summing ΔW over entire process we get total work done by gas so we have�W=∫^V2_V1PdV where limits of integration goes from V₁ to V₂�as PV=nRT we have P=nRT/V�Therefore W=∫^V2_V1 (nRT/V)dV�On integrating we get, W=nRTln(V₂-V₁)�Where n is number of Moles in sample of gas taken.�and ln=loge

This can be also written as�W=2.303nRTlog(V₂/V₁) �

This can also be expresses in terms of Initial Pressure and Final Pressure also  W=2.303nRTlog(P₁/P₂)

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PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD

Que. Can the value of specific heat of a gas be infinity?

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Ans. Yes

THANK YOU�PREPARED BY:��S D KHOBRAGADE�PGT PHYSICS�JNV OSMANABAD�

PREPARED BY: S D KHOBRAGADE PGT PHYSICS JNV OSMANABAD