Thermodynamic Concepts of Metallurgy Chemistry Notes
Thermodynamic Principales of Metallurgy :
→ Some basic principles of thermodynamics help us to understand the theory of metallurgical transformations. Gibbs energy is the most significant term for this purpose. For any process, the change in Gibbs energy at any specific temperature, can be explained with the help of this equation.
AG = ∆H – T∆S
where, ∆G =Change in Gibbs free energy
∆H = Change in enthalpy
∆S-Change in entropy
T = temperature in Kelvin
For any reaction, this change in Gibbs free energy can also be explained with the help of equation given below:
∆G = – RT In K
∆G = -2.303 RT log K
where, K-Equilibrium constant for the ‘reactant product system
T – Temperature in Kelvin
R – Gas constant.
→ If the value of Gibbs free energy is negative then it implies the positive value of equilibrium constant K. But it happens only when the reaction proceeds towards products. From the above given facts, we can make the following conclusions :
→ When the value of ∆G is negative, only then the reaction will proceed in forward direction or will form products. If the value of ∆S is positive, then on increasing the temperature T, the value of T∆S will also increase (∆H < T∆S) and then the value of ∆G will become negative.
→ If reactants and products of two reactions are put together in a system and the net ∆G of the two possible reactions is negative then the overall reaction will occur. In this condition, coupling of two reactions will occur. In other words, we can say that if the value of ∆G is positive for any reaction then this reaction should be coupled with other reaction which has -ve value of ∆G. So, that the sum of Gibbs free energies of coupled reaction may become negative.