Principles Of Physical Chemistry - Chapter 13: The First Law Of Thermodynamics PDF

# PRINCIPLES OF PHYSICAL CHEMISTRY ## CHAPTER 13: THE FIRST LAW OF THERMODYNAMICS **Smectic phase:** Molecules are arranged in nearly parallel layers. * The layers are held at regular distances from one another * Molecules within each layer are not regularly spaced. * Anisotropic properties (lik...

# PRINCIPLES OF PHYSICAL CHEMISTRY ## CHAPTER 13: THE FIRST LAW OF THERMODYNAMICS **Smectic phase:** Molecules are arranged in nearly parallel layers. * The layers are held at regular distances from one another * Molecules within each layer are not regularly spaced. * Anisotropic properties (like double refraction) can be understood. **Nematic phase:** Molecules are in parallel but there are no layers. * Arrangement is irregular * Molecules have greater freedom of motion. **Normal liquid:** Molecules move completely at random, there is no double refraction, and the material is isotropic. **Industrial Lubricants:** Most industrial lubricants exist in the mesomorphic (liquid crystal) state. * Their functioning as lubricants is due to their existence in this state. * Proteins and fats (important constituents of food) also exist in this state before digestion. **Liquid Crystal Display Devices (LCDs):** Nematic and smectic types of liquid crystals are widely adopted for LCDs. * They operate through their interaction with natural light, either in transmission or reflection. * They consume very little power. **Thermodynamics:** This term implies flow of heat. The subject is concerned with energy changes accompanying all types of physical and chemical processes. ### Importance of Thermodynamics * Most important generalisations of physical chemistry can be deduced from the laws of thermodynamics, including: * van't Hoff Law of Dilute Solutions * Raoult's law of vapour pressure lowering * Distribution law * Law of chemical equilibrium * Phase rule * Laws of thermochemistry * Thermodynamics helps to lay down the criteria for predicting feasibility (or spontaneity) of a process. * Helps to predict whether a given process (or a chemical reaction) is feasible under given conditions. * Helps to determine the extent to which a process can proceed before attaining equilibrium. ### Limitations of Thermodynamics * The laws of thermodynamics apply only to matter in bulk.  * The laws apply to the collective behavior of many molecules but not to individual molecules. * Thermodynamics can predict feasibility but does not predict the rate at which a change occurs. ### Basic Terms in Thermodynamics * **System:** Any specified portion of matter under study which is separated from the rest of the universe with a bounding surface. * **Surroundings:** The rest of the universe (usually the air or a water bath) which might be in a position to exchange energy and matter with the system. * **Isolated System:** A system which can exchange neither energy nor matter with its surroundings. * **Closed System:** A system which can exchange energy but not matter with its surroundings. * **Open System:** A system which can exchange both matter and energy with its surroundings. * **Macroscopic Properties:** Properties associated with a macroscopic system; these include pressure, volume, temperature, composition, density, viscosity, surface tension, refractive index etc. * **Homogeneous System:** A system that is completely uniform throughout, containing only one phase. * Examples: A pure solid, a liquid, a solution, a mixture of gases. * **Heterogeneous System:** A system which is not uniform throughout, containing two or more phases. * Examples: Two or more immiscible liquids, a solid in contact with a liquid where it doesn't dissolve. * **Phase:** A homogeneous and physically distinct part of a system, bounded by a surface and mechanically separable from other parts. * **State of a System:** When macroscopic properties of a system have definite values, the system is said to be in a definite state. * **State Variables:** The macroscopic properties of a system, such as Pressure, temperature, volume, mass and composition. * **Extensive Properties:** Properties that depend upon the amount of substance present (mass, volume, energy) * **Intensive Properties:** Properties that are independent of the amount of substance present (temperature, pressure, density, viscosity). * **Thermodynamic Processes:** The operation by which a system changes from one state to another. * **Isothermal Process:** The temperature of the system remains constant during each stage of the process. * **Adiabatic Process:** No heat enters or leaves the system during any step of the process. * **Isobaric Process:** The pressure of the system is constant during each step of the process. * **Reversible Process:** A process carried out infinitesimally slowly, where the driving force is only infinitesimally greater than the opposing force. * Almost all processes occurring in nature or laboratory are irreversible. * **Irreversible Process:** Any process which does not take place in this manner and requires time for completion. ### Thermodynamics and Energy * **Joule:** The unit of energy in the SI system. Work done when a resistance of 1 newton is moved through a distance of 1 metre. * **Mechanical Equivalent of Heat:** The relationship between work and heat. W=JH (British physicist James P. Joule (1818-1889)) * **Internal Energy:** The total energy associated with a substance or system, which is a definite quantity dependent on the state of the system. * **First Law of Thermodynamics:** Energy can neither be created nor destroyed but can be transformed from one form to another. * **Conservation of Energy:** Whenever energy in one from disappears an equal amount of energy in some other form must appear. * **Heat Capacity.** Defined as the quantity of heat (q) required to raise the temperature of the system through 1°C. ### Enthalpy * **Enthalpy:** The total energy stored in the system (U+PV) * **Enthalpy of Vaporisation:** The change in enthalpy when a liquid evaporates or vapors condense. * **Enthalpy of Fusion:** The change in enthalpy when a solid melts or a liquid freezes. ### Work Done * **Work Done in Reversible Isothermal Expansion:** -RTln(V2/V1) or -RTln(P1/P2) * **Work Done in Reversible Isothermal Compression:** -RTln(V1/V2) or -RTln(P2/P1) * **Work Done in Free Expansion (Expansion Against Vacuum):** 0 * **Work Done in Irreversible Isothermal Expansion against a Constant Pressure:** -P(V2 -V1) ### Adiabatic Process * **Adiabatic Expansion:** q=0, w=AU, AU is negative. * **Adiabatic Compression:** q=0, w=AU, AU is positive. * **Final Temperature in Reversible Adiabatic Expansion:** Cv ln(T2/T1) = Rln (V2/V1) * **Final Temperature in Irreversible Adiabatic Expansion:** Can be calculated knowing Pext, Cy, T1, T2, P1, P2, ### Other Concepts * **The Cyclic Rule** * **Joule-Thomson Effect:** The phenomenon of change of temperature produced when a gas is made to expand adiabatically from a region of high pressure to a region of low pressure. * **Inversion Temperature:** The temperature below which a gas becomes cooler on expansion. * **Joule-Thomson Coefficient:** The rate of change of temperature with change of pressure under adiabatic conditions. * **Zeroeth Law of Thermodynamics:** If body "A" is in equilibrium with body "C" and body "B" is in equilibrium with body "C", then "A" and "B" are also in equilibrium with each other. * **Absolute Temperature Scale:** Based on the observation that PV - P graphs of all real gases when extrapolated to zero pressure give the same value of PV at a given temperature. * The value is denoted by (PV) in general and by (PVm) for one mole of a gas.. * The value of (PVm)0 is zero at - 273.15 °C or 0 Kelvin (K)