Chapter 1 The first law of thermodynamics § 1.1 Basic introduction

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.

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.

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?

Heat flow High T Low T Work To power our modern civilization, we need to know the relationship between chemistry and energy.

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

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

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

(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 K, with the volume of 22.4 dm 3 and mass of 2 g. example

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)

The zeroth law of thermodynamics: Definition of temperature

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

Is there any relationship between state functions? 1 mol of hydrogen gas at 1 p  and 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?

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.

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

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!

(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

(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

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