Thermodynamics (first and second laws)

ByAravin Prince.P,

First- M.Tech- Textile Tech,KCT.

Introduction of first law

It is a subject dealt with volume, pressure, temperature,

and concentration and with the relationships between

them

The first law prediction is however concern only the

difference between the “ initial and final states” of the

change in the internal energy.

In dyeing is involving with the color physics like which

dye is adsorbed from solution by a substrate, but only

with the end product.

Contd…

The first law of thermodynamics is dealtwith three fundamental concepts namely“Energy, Work & Heat” and relationshipamong them.

Energy Thermodynamics is concerned with “internal energy

U” , that is energy acquired by means of the mass and

motions of molecules , intermolecular forces and

chemical compositions.

The energy equation is

∆U=U2-U1

Where ..,

∆U= Total energy

U1 =Initial value of the internal energy system

U2 =Final value of the internal energy system

Work

Work may be defined as the energy lost from

the system other than by heat transfer

Basically work is known as pressure- volume

or PV work

Volume change is represent by ∆V, then the

work done is given by

W=p ∆V

First law derivation

The first principle of thermodynamics

states that the internal energy E of the

system is closed. i.e it cannot exchange

material with an external environment, it

is defined as follows

∆E=q-w

Q= heat absorbed by the system

W= work done of the system

At the constant volume the work of expansion is zero and so

∆E=q

At constant pressure work is

w=P. ∆V

Then the heat is equal

∆E+P. ∆V

Normally the reaction heat in these conditions is given the name

of enthalpy or thermic content (represented by H), then the

equ..,

∆H= ∆E+P. ∆Vq

Thermodynamics reminds us that the enthalpy of a reaction is

∆H=Hproducts-Hdyes

∆H value is –ve = reaction is exothermic

∆H value is +ve = reaction is endothermic

Second law of thermodynamics

It is defined as a spontaneous process in an isolated

system there is an increase in entropy ; the entropy

change occurring during the process, ∆S is positive

Then the equ..

dq (rev)

dS= -------------

T

Q= heat absorbed

T= Temp of the system

And for irreversible spontaneous process

dq (irrev)dS > -------

T

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