Thermodynamics (first and second laws) By Aravin 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 dealt with three fundamental concepts namely “Energy, Work & Heat” and relationship among 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-U1Where .., ∆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-wQ= heat absorbed by the systemW= work done of the system
At the constant volume the work of expansion is zero and so ∆E=qAt constant pressure work is w=P. ∆VThen the heat is equal ∆E+P. ∆VNormally the reaction heat in these conditions is given the name of enthalpy or thermic content (represented by H), then the equ.., ∆H= ∆E+P. ∆VqThermodynamics 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= ------------- TQ= heat absorbedT= Temp of the system
And for irreversible spontaneous process dq (irrev) dS > ------- T