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Chapter 1 The first law of thermodynamics § 1.1 Basic introduction
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A macroscopic science, the study of two physical quantities, energy and entropy. Particularly concerns with the interconversion of energy as heat and work. 1.1 Thermodynamics: What is chemical thermodynamics? A branch of physical chemistry that studies the energy conversion during chemical processes. Problem: find the three definitions of thermodynamics in the textbook.
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Energy: reservation and conversion Electricity: coal (chemical energy) combustion (in a burner, heat / thermal energy is produced) expansion of gas (drives piston in a turbine, work, mechanical energy) electricity (rotator in generator, electric energy) Transportation: oil (chemical energy) combustion (burn in an engine, heat, thermal energy) expansion of gas (work, mechanical energy) movement (dynamic energy) CO 2, NO x CO 2, SO 2 What is energy? Energy is the capacity to do work or to produce heat.
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The problem was put forward due to study of thermal machine: turbine. Heat out Heat in Work in / out How do we study the transfer of energy?
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Heat flow High T Low T Work To power our modern civilization, we need to know the relationship between chemistry and energy.
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System: The parts of universe under study. Surroundings: The parts of the universe that interacts with the system 1.2 Some basic concepts Water: open system Cup: open system Box: closed /isolated system Boundary/wall: real or imaginary; rigid or nonrigid, permeable or impermeable Selection of system (1) System and surroundings
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open system Closed system Isolated system Energy Matter Energy Matter Energy Matter thermal conducting Adiabatic; Nonadiabatic What kind of system is the button battery? (2) Kinds of system
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1) Mechanical equilibrium Four Equilibriums 3) Chemical equilibrium 2) Thermal equilibrium 4) Phase equilibrium (3) System at equilibrium: the way we define the system p, T, c System at equilibrium: The properties of the system such as the pressure (p), temperature (T), composition and concentration (c, and p B ) and the number of phases do not change with time. Equilibrium thermodynamics
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(3) State and state functions The overall behavior of the system is state. The physical and chemical quantities used to describe the state of the system is state function. 1 mol of hydrogen gas at 1 p and 273.5 K, with the volume of 22.4 dm 3 and mass of 2 g. example
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State functions used for describe the system: Composition: mass (m), number of substance (n), Geometric: area (A), volume (V) ; Mechanical: pressure (p), surface tension ( ), density( ) Chemical: the amount of substance (n), molality (m), molarity (c), molar fraction (x) Electromagnetic: current density (I), strength of electric field (E) ; Thermodynamic: temperature (T), enthalpy (H), internal energy (U), Holmholtz’s function (F), Gibbs’ function (G)
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The zeroth law of thermodynamics: Definition of temperature
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Extensive property : The value of the property changes according to the amount of substance which is present (e.g., mass, volume, internal energy ) Intensive property : The value of the property is independent of the amount of substance which is present (e.g., temperature, density ) Propertiesextensiveintensive QuantityVolume (V), the amount of substance (n), mass (m), Pressure (p), concentration (c), density ( ), heat capacity (C), dielectric constant ( ), etc. RatioMolar mass (M), molar volume (V) Scalar or vector We usually don’t consider electric, magnetic, gravitational field
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Is there any relationship between state functions? 1 mol of hydrogen gas at 1 p and 273.5 K, with the volume of 22.4 dm 3 and mass of 2 g. Basically, we can define the state of a single-component system using only three state functions: the amount of substance, pressure and temperature, i.e., n, T, p. Need we define all the state functions of a system to describe the system?
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For a closed single-component system with known amount of substance, we need only pressure and temperature, i.e., T, p. For a multi-component system, we need the amount of each component, n 1, n 2 n S, and pressure and temperature. One extensive property and two intensive properties.
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1) The value of a particular state function for a system depends solely on the state of the system. Once the state is set, all the state functions will have a definite value. And the state function difference between two different states only depends on the initial and final state of a process. Important properties of state function 4 m
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State functions have overall differential. For state function p 1, T 1 History ? Future ? A glass of water is now at 50 o C. Did it cool from 100 o C? Or was it heated from 25 o C? No one knows!
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(4) Path functions: A property depends upon the path by which a system in one state is changed into another state. Are you strong enough to jump 4 m high in one jump? Certainly not. But I can attain that height step by step! 4 m
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(5) Processes: p 1, T 1 p 2, T 2 Initial stateFinal state p 2, T 1 p 1, T 2 isotherm Isobar Isotherm; Isobar; Cycle; Reversible; Adiabatic
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Summary System vs. surroundings Classification of systems: open, closed, isolated; System equilibriums: mechanical, temperature, chemical and phase State and state function: Extensive state function vs. intensive state function state function vs. process function Processes: isotherm, isobar, cycle, reversible, adiabatic
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