THERMODYNAMICS

PRADEEP GUPTA(NITA)

THERMODYNAMICS

The name thermodynamics stems from the Greek words therme (heat) and dynamis (power), which is most descriptive of the early efforts to convert heat into power.

Thermodynamics is the branch of science which deals with the relation between heat and other form of energy.

BASIC LAWS OF THERMODYNAMICS

.

ZEROTH LAW OF THERODYNAMICS

It states that if a body ‘A’ be in thermal equilibrium with another body ‘B’ and also with thermal equilibrium with a third body ‘C’ then boy ‘B’ will also be thermal equilibrium with third body ‘C’.

FIRST LAW OF THERMODYNAMICS

First law of thermodynamics basically is the conversation of energy. It states that “energy can neither be created nor destroyed but it can only transfer from one form of energy to another”

SECOND LAW OF THERMODYNAMICS

Second law of thermodynamics has been mentioned by two statements

Classius Statement: “It states that it is impossible to make an device which produces no effect other then transfer the heat from a cold body to a hot body”.

Kelvin-Plank Statement: “It states that it is impossible foe a heat engine to produce work in complete cycle if it exchanges heat only with body at a single fixed temperature.

THIRD LAW OF THERMODYNAMICS

It is also called Nerst-Simon Statement. It states that “It is impossible by any

procedure no matter how idealized to reduce any system to absolute zero of temperature in finite number of operations.

PERPETUAL MOTION MACHINE (PPM)

PPM of first kind: “ There can be no machine which would continuously supply mechanical work without some other form of energy disappears simultaneously.

PPM of second kind: “There can be no machine which would exchange heat from single reservoir and do equal amount of work.”

These are fictitious machines.

BASIC CONCEPTS OF THERMODYNAMICS System: A quantity of matter in space

which is analysed during a problem. Surroundings: Everything external to

the system. System Boundary: A separation

present between system and surrounding.

BASIC CONCEPTS OF THERMODYNAMICS

Intensive property: Whose value is independent of the size or extent i.e. mass of the system.These are, e.g., pressure p and temperature T.

Extensive property: Whose value depends on the size or extent i.e. mass of the system (upper case letters as the symbols). e.g., Volume, Mass (V, M). If mass is increased, the value of extensive property also increases. e.g., volume V, internal energy U, enthalpy H, entropy S, etc.

Specific property: It is a special case of an intensive property. It is the value of an extensive property per unit mass of system. (Lower case letters as symbols) eg: specific volume, density (v, ρ).

BASIC CONCEPTS OF THERMODYNAMICS Intensive and Extensive Properties:- There are certain properties which depend on the size or extent of the system, and there are certain properties which are independent of the size or extent of the system. The properties like volume, which depend on the size of the system are called extensive properties. The properties, like temperature and pressure which are independent of the mass of the system are called intensive properties.

THERMODYNAMICS EQUILIBRIUM

a. Thermal equilibrium A state of thermal equilibrium can be described as one in which the temperature of the system is uniform.

b. Mechanical equilibrium Mechanical equilibrium means there is no unbalanced force. In other words, there is no pressure gradient within the system.

c. Chemical equilibriumThe criterion for chemical equilibrium is the equality of chemical potential

Superscripts A and B refers to systems and subscript i refers to component

THERMODYNAMIC PROCESSES

Process:- In thermodynamics we are mainly concerned with the systems which are in a state of equilibrium. Whenever a system undergoes a change in its condition, from one equilibrium state to another equilibrium state, the system is said to undergo a process.

A process is said to be reversible if the system and its surroundings are restored to their respective initial states by reversing the direction of the process. A reversible process has to be quasi-static, but a quasi - static process is not necessarily quasi-static.

THERMODYNAMIC PROCESSES

A process in which the volume remains constant is called constant volume process. Also called isochoric process / isometric process

A process in which the pressure of the system remains constant is called constant pressure process. Also called isobaric process

A process in which the temperature of the system is constant is called constant temperature process. Also called isothermal process

A process in which the system is enclosed by adiabatic wall is called Adiabatic process

WORK AND ENERGY Work is one of the basic modes of energy

transfer. The work done by a system is a path function, and not a point function. Therefore, work is not a property of the system, and it cannot be said that the work is possessed by the system.

Energy is often defined as the capacity to produce work. Energy is a property of the system

HEAT Heat:- Heat is energy transfer which occurs

by virtue of temperature difference across the boundary. Heat like work, is energy in transit. It can be identified only at the boundary of the system. Heat is not stored in the body but energy is stored in the body. Heat like work, is not a property of the system and hence its differential is not exact. Heat and work are two different ways of transferring energy across the boundary of the system.

IST LAW OF THERMODYNAMICS FOR A PROCESS For a process: according to first

law

For a cyclic process

Q=W+∆U

=

WORK DONE IN A PROCESS

In constant volume processWork done (W)= 0;Heat transferred (Q)= change in internal energy energy(U)= m*cv *(T2-T1)

In isobaric process work done(dW)= Heat transfer(dQ)= m*cp*dt

Internal energy(dU)=dQ-dW

WORK DONE IN A PROCESS

In isothermal process Work done (W)= m**T = Heat transferred (Q);change in internal energy energy(U)= 0;

In reversible adiaatic process work done(W)=Heat transfer(Q)= 0;Internal energy(U)=-W

=ratio of specific heats

CLASSIUS INEQUALITY For a cyclic process it is proved that

If then cycle is irreversible. then cycle is reversible. no such cycle is possible.

ENTROPY It may e noted that total heat is not

equally valuable for converting into work. Entropy plays a vital role in heat engine theory. It can be defined as” Entropy is a function of quantity of heat which shows the possibility of conversion of heat into work.”

In other words, “Entropy shows the randomness of molecules.”

ENTROPY CONT….

Entropy is a property of a system and is a Extensive property. Mathematically-

∆Suniverse=0 then cycle is reversible.

∆Suniverse<0 then cycle is irreversible.

ds=R

ENTROPY CONT…. This integration can e performed only

for reversible processes. Also for adiabatic process dQ=0;And if it is reversible then ds=0;So reversible adiabatic process is known as isentropic process.

ENTROPY CONT…

Entropy increases of ice as it is heated from -T0C to 00C at 1 atm.

Entorpy increases of melting of water

Entropy increases of water as it is heated from 00C to T0C at 1 atm.

∆S==

∆S== L= latent heat of melting

= specific heat of ice

ENTROPY CONT…

Entorpy increases of melting of water

Entropy increases of water as it is heated from 00C to T0C at 1 atm.

∆S==

∆S==

∆S==

L’= latent heat of vaporasion

= specific heat of water vapour

= specific heat of water

HEAT ENGINE A device which can be produce work

continuously ( which operates on cyclic process) at expanse of heat input is called heat engine.

ɳ== For reversible cycle

ɳ==

REFRIGERATORS A refrigerators is a device operating on

a cycle which removes heat from low temperature body and reject it to a body at higher temperature at the expanse of external work supply. The objetive of the system is to produce cooling effect at low temperature.

(COP)R== orCOP)R == (only for

reversible processes)

HEAT PUMPS A heat pumps is a device

operating on a cycle which removes heat from low temperature body and reject it to a body at higher temperature at the expanse of external work supply. The objective of the system is to produce heating effect at low temperature.(COP)H== orCOP)H == (only for

reversible processes)

CARNOT CYCLE Carnot cycle: It consists two adiabatic and

two isothermal processes. Carnot theorem: it states that any heat

engine operating on a cycle between two heat reservoir at different fixed temperatures limit cannot more efficient then a reversible cycle.

Corollary : It states that efficiency of all reversible engine operating between same temperatures limit is same.

PURE SUSTANCES

A substance of constant chemical composition through out its mass is called pure substance.

Triple point :- The only state at which the solid, liquid and vapor phase coexist in equilibrium.

Critical State:- If we keep on increasing the pressure a state comes when solid will directly converted into gasous state without coming in liquid state. This is known as critical state.

Latent heat of vaporization ecomes zero at critical state.

THEORY OF IDEAL GAS

An ideal gas is defined as a gas having no force of intermolecular attraction. Real gases almost behaves as an ideal gas at low pressure and high temperature.

Boyle’s law: pα T= constant.

Charles’ law: vαT p= constant.

THEORY OF IDEAL GAS

Ideal gas equation:

Where R= (characterastic gas constant)Ṝ= universal gas constant = molecular weightm= mass of gasn= number of mole of gas

pv= mRTpv= nṜT

REAL GAS EQUATION

Vanderwaal’s Equation

(p+)(v-b)=RTWe can simplify this equation as

p=–Berthelot Equation

p=–

REAL GAS EQUATION

Dirterici Equation

p= Redlich-Kwong Equation

p=– Saha-Bose Equation

p=

SPECIFIC HEAT OF GASES

cv = specific heat of gas at constant volume

cp=specific heat of gas at constant pressure

cp-cv=R (Mayer formula)

=ɣ cv = cp =

.……….

THANK YOU