Uph012: Biophysics And Biomaterials Lecture Notes PDF

1/15 UPH012: Biophysics and Biomaterials Purely for teaching purpose only 1 Disclaimer: The materials used in this presentation have purely teaching purposes only. Purely for teaching purpose only 2 ...

1/15 UPH012: Biophysics and Biomaterials Purely for teaching purpose only 1 Disclaimer: The materials used in this presentation have purely teaching purposes only. Purely for teaching purpose only 2  Biophysics and Biomaterials Thermodynamics and diffusion Kinetics: Free energy, internal energy, concept of equilibrium, stability and metastability, basic thermodynamic functions, statistical nature of entropy, kinetics of thermally activated process, Fick’s law of diffusion, solution to Fick’s second law and its applications, Kirkendall effect, atomic model of diffusion. Purely for teaching purpose only 3  Thermodynamics One branch of knowledge that all engineers and scientists must have a grasp of (to some extent or the other!) is thermodynamics. Thermodynamics can be considered as a ‘system level’ science- i.e. it deals with descriptions of the whole system and not with interactions (say) at the level of individual particles. It deals with quantities (like T, P) averaged over a large collection of entities (like molecules, atoms). This implies that questions like: “What is the temperature or entropy of an atom?”; do not make sense in the context of thermodynamics. Purely for teaching purpose only 4  Thermodynamics ❑ Thermodynamics deals with stability of systems. It tells us ‘what should happen?’. ‘Will it actually happen(?)’ is not the domain of thermodynamics and falls under the realm of kinetics. ❑ At –5C at 1 atm pressure, ice is more stable then water. Suppose we cool water to –5C. “Will this water freeze?” (& “how long will it take for it to freeze?”) is (are) not questions addressed by thermodynamics. System is region where we focus our attention. Surrounding is the rest of the universe Universe = System + Surrounding. Purely for teaching purpose only 5  Thermodynamics System Closed Open Isolated Surrounding Heat Temperature, Equilibrium Biological systems are open systems Purely for teaching purpose only 6  Thermodynamics System Closed Open Isolated Surrounding Heat Temperature, Equilibrium Purely for teaching purpose only 7  Biological Thermodynamics What is energy? “…the term energy is difficult to define precisely, but one possible definition might be the capacity to produce an effect” Encyclopædia Britannica Purely for teaching purpose only 8 Biological Thermodynamics Purely for teaching purpose only 9  Biological Thermodynamics The First Law of thermodynamics The total energy of the universe is constant, no matter what changes occur within. Energy can be changed from one form to another, but in all its transformations energy is neither created nor destroyed. This principle also applies to an isolated system. Purely for teaching purpose only 10  Biological Thermodynamics Internal Energy (U) Is the energy within the system? The internal energy of a system is the total kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the total potential energy associated with the vibrational and electric energy of atoms within molecules or crystals. U is a state function (the energy difference is independent of path), that is, its value depends only on the current state of the system ΔU = U2 – U1 For a complete cycle (a change from state 1 to state 2 and back again): ΔU = 0 Purely for teaching purpose only 11  Biological Thermodynamics Work (w) and Heat (q) ΔU = w + q Unlike the internal energy, both heat and work are represented by lower case symbols. This is because U is a state function, but neither q nor w is a state function. Instead, q and w are path Work involves the non-random Heat involves the random functions. movement of particles movement of particles Purely for teaching purpose only 12  Biological Thermodynamics Work (w) and Heat (q) According to the First Law of Thermodynamics. (food intake) – (waste excreted) = (change in body weight) + (heat) + (work), Purely for teaching purpose only 13  Biological Thermodynamics Work (w) and Heat (q) Sign conventions for heat and work Heat is transferred to the system q>0 Heat is transferred to the surroundings q0 The forward reaction is energetically unfavorable; the reverse reaction proceeds spontaneously ΔG=0 The system is at equilibrium, there is no further change ΔG 0, mixing When 𝑡→∞ , free energy, minimum occurs minimum free energy, entropy. maximum entropy. Equilibrium state corresponds to the completely mixed state which has a minimum of free energy and a maximum of entropy. Purely for teaching purpose only 33  Biological Thermodynamics Gibbs free energy (G) G is a sort of combination of the First and Second Laws, as it involves both enthalpy and entropy. G = H -TS Change in ΔG ΔG = ΔH – SΔT – TΔS ……….(i) At constant temperature ΔG = ΔH – TΔS ………(ii) Since pV-work only be done in a reversible system ∆𝑈 = 𝑇∆𝑆 − 𝑝∆𝑉 𝐻 = 𝑈 + 𝑝𝑉 ∆𝐻 = ∆𝑈 + 𝑝∆𝑉 + 𝑉∆𝑝 On substituting above equation in equation (i) ∆𝐺 = 𝑇∆𝑆 − 𝑝∆𝑉 + 𝑝∆𝑉 + 𝑉∆𝑝 − 𝑇∆𝑆 − 𝑆∆𝑇 34 Purely for teaching purpose only  Biological Thermodynamics On simplification ∆𝐺 = 𝑉∆𝑝 − 𝑆∆𝑇 At constant pressure (p) and temperature (T) ΔG = 0. For reversible systems has maximal or minimal value of G when T and p are constant and the system is at equilibrium. For any real process to occur spontaneously at constant temperature and pressure, the Gibbs free energy change must be negative. The magnitude of ΔG tells us the size of the driving force in a spontaneous reaction, ΔG says nothing at all about the time required for the reaction to occur. Purely for teaching purpose only 35