Physical Pharmacy I Lecture 7 Thermodynamics PDF

Physical Pharmacy I Lecture 7 Thermodynamics, first, second and Third law, thermochemistry 11 October, 2024 Physical Pharmacy I 1 Introduction...

Physical Pharmacy I Lecture 7 Thermodynamics, first, second and Third law, thermochemistry 11 October, 2024 Physical Pharmacy I 1 Introduction What is Thermodynamics? ØThermodynamics is the study of the relationships between heat, work, energy, and matter. ØIt is essential to comprehend how energy is transformed and matter behaves on a macroscopic scale. 2  The First Law of Thermodynamics ØThe first law states that energy cannot be created or destroyed, only transferred or converted. ØIt's often expressed as ∆U = Q – W where ∆U is the change in internal energy, Q is heat, and W is work. ØThis law underpins the principle of energy conservation. 3 ØThermochemistry deals with the heat changes that occur during chemical reactions. ØEnthalpy (∆H) is a central concept, representing the heat exchanged at constant pressure. ØThermochemical equations are used to calculate ∆H, helping us understand reaction energetics. ØA thermochemical equation is a type of balanced chemical equation in which the amount of energy absorbed or released during a chemical reaction is included. Combustion of methane: C H 4 ( g ) + 1 2 O 2 ( g ) ⟶ C O 2 ( g ) + 2 H 2 O ( l ) Δ H = − 890.3 k J. Formation of water: H 2 ( g ) + 1 2 O 2 ( g ) ⟶ H 2 O ( l ) Δ H = − 285.8 k J. Melting of ice: H 2 O ( s ) ⟶ H 2 O ( l ) Δ H = + 6.00 k J + Δ H = Endothermic reaction - Δ H = Exothermic reaction 4  Examples to illustrate the Second Law Diffusion of Perfume: ØOpen a bottle of perfume in one corner of a room. ØEventually, the scent molecules disperse throughout the room, and you can smell the perfume from any location. ØThe spontaneous mixing of perfume molecules represents an increase in entropy, as they spread out evenly. Melting Ice Cube: ØConsider an ice cube in a glass of water at room temperature. ØAs time passes, the ice cube melts, and the cold ice water mixes with the warmer water. ØThis process increases the overall entropy in the system, as the initially ordered state (separate ice and water) transforms into a more disordered state (mixed water). 5 The Third Law of Thermodynamics Ø“the entropy of a system approaches a constant value as the temperature approaches absolute zero”. ØAbsolute zero is the point at which molecular motion ceases entirely. ØAccording to the Third Law of Thermodynamics, as the crystal approaches absolute zero, its entropy approaches a minimum value, which is typically zero. ØEntropy is a measure of the disorder or randomness in a system, and at absolute zero, there is no thermal motion of particles, making the system as ordered as it can possibly be. 6  The Third Law of Thermodynamics ØSuperconductivity is a phenomenon in which certain materials, when cooled to very low temperatures, exhibit zero electrical resistance e.g. MRI machines, particle accelerators, and efficient power transmission lines. ØThis law is essential for understanding the behaviour of materials at very low temperatures. 7 Free Energy Function Gibbs free energy (G) and Helmholtz free energy (A) are functions that describe a system's ability to do work at constant temperature and pressure. ∆G = ∆H - T∆S ∆G is the change in Gibbs free energy. ∆H is the change in enthalpy (heat) of the system. Enthalpy Change (∆H): If the energy required to break the bonds is greater than the energy released when forming the new bonds, ∆H is positive (endothermic reaction). If the energy released is greater, ∆H is negative (exothermic reaction). T is the temperature in Kelvin. ∆S is the change in entropy (refers to the disorder or randomness in the system). helps predict whether a reaction is spontaneous (∆G < 0) or non-spontaneous (∆G > 0) 8  Thank you 9