Chapter 1 The first law of thermodynamics § 1.1 Basic introduction.

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)

CO2, NOx

CO2, SO2

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 equilibriumFour

Equilibriums 3) Chemical equilibrium2) 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 pre

ssure (p), temperature (T), composition and

concentration (c, and pB) 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 273.5 K,

with the volume of 22.4 dm3 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), mola

rity (c), molar fraction (x)

Electromagnetic: current density (I), strength of electric fi

eld (E) ;

Thermodynamic: temperature (T), enthalpy (H), internal e

nergy (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)

Properties extensive intensive

Quantity Volume (V), the amount of substance (n), mass (m),

Pressure (p), concentration (c), density (), heat capacity (C), dielectric constant (), etc.

Ratio Molar mass (M), molar volume (V)

Scalar or vector

We usually don’t consider electric, magnetic, gravitational field

Is there any relationship between state functions?

pV nRT ( , )V V p T

1 mol of hydrogen gas at 1 p and 273.5 K,

with the volume of 22.4 dm3 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, n1, n2nS, 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

p T

dV dV dVdT dp

dT dT dp

State functions have overall differential.

( , )V V p T

For state function

p1, T1

History ? Future ?

A glass of water is now at 50 oC. Did it cool from

100 oC? Or was it heated from 25 oC?

No one knows!

(4) Path functions: A property depends upon the path by which a system in o

ne 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:

p1, T1 p2, T2 Initial state Final state

p2, T1

p1, T2

isotherm

isotherm

Isobar

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