Transcript Document

Chapter 1 The first law of
thermodynamics
§1.1 Basic introduction
1.1 Thermodynamics:
What is chemical thermodynamics?
A branch of physical chemistry that studies the energy
conversion during chemical processes.
A macroscopic science, the study of two physical quantities,
energy and entropy.
Particularly concerns with the interconversion of energy as
heat and work.
Problem: find the three definitions of thermodynamics in the
textbook.
Energy: reservation and conversion
What is energy?
Energy is the capacity to do work or to produce heat.
Electricity:
CO2, SO2
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:
CO2,
NOx
oil (chemical energy)  combustion (burn in an engine, heat,
thermal energy)  expansion of gas (work, mechanical energy)
 movement (dynamic energy)
How do we study the transfer of
energy?
The problem was put
forward due to study of
thermal machine: turbine.
Heat out
Work in / out
Heat in
High T
To power our modern civilization, we
Heat
flow
Work
need to know the relationship between
chemistry and energy.
Low T
1.2 Some basic concepts
(1) System and surroundings
System: The parts of universe under study.
Surroundings: The parts of the universe that interacts
with the system
Boundary/wall: real or imaginary;
rigid or nonrigid, permeable or
impermeable
Water: open system
Cup: open system
Box: closed /isolated system
Selection of system
(2) Kinds of system
Energy open
Matter system

Energy Closed
Matter system
 Energy
 Matter
Isolated
system
thermal conducting
Adiabatic;
Nonadiabatic
What kind of system
is the button battery?
(3) System at equilibrium: the way we define the
system
1) Mechanical equilibrium
Four
Equilibriums
2) Thermal equilibrium
3) Chemical equilibrium
4) Phase equilibrium
Equilibrium thermodynamics
System at equilibrium:
p, T, c
The properties of the system such as the
pressure (p), temperature (T), composition
and concentration (c, and pB) and the
number of phases do not change with time.
(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.
example
1 mol of hydrogen gas at 1 p and 273.5 K,
with the volume of 22.4 dm3 and mass of 2 g.
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)
Properties
Quantity
extensive
intensive
Volume (V), the
Pressure (p), concentration (c),
amount of substance density (), heat capacity (C),
(n), mass (m),
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?
1 mol of hydrogen gas at 1 p and 273.5 K,
with the volume of 22.4 dm3 and mass of 2 g.
pV  nRT
V  V ( p, T )
Need we define all the state functions of a system to
describe the system?
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.
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, n2nS, and pressure and temperature.
One extensive property and two intensive properties.
Important properties of state function
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.
4m
For state function
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!
Future ?
History ?
p1, T1
V  V ( p, T )
 dV 
dV  dV 

 dp
 dT  
dT  dT  p
 dp T
State functions have overall differential.
(4) Path functions:
A property depends upon the path by which a system
in one state is changed into another state .
4m
Are you strong enough to jump 4 m high in one jump?
Certainly not. But I can attain that height step by step!
(5) Processes:
p 2 , T1
isotherm
Isobar
Isotherm;
Isobar;
Cycle;
Reversible;
Adiabatic
Initial state
p 1 , T1
Final state
p 2 , T2
isotherm
Isobar
p 1 , T2
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