Transcript Document

Chapter 6
The First Law of
Thermodynamics
6.1 Work. Internal Energy.
And Heat
 1.Work
 In thermodynamics work is defined
as energy transfer across the
boundary of a system .Work is
assigned the symbol W.
Kinds of Work:
 The work to vary the volume of a
system
 Surface work
 Electrical work
 Magnetic work
 2.Internal Energy
 The function of states
 3.Heat
 Energy can be transported across the
boundary in two distinct forms: heat and
work.
 Energy transported across a boundary as
a result of a temperature difference
between a system and its surroundings is
called heat.
6.2 The First Law of
Thermodynamics
 The Foundation of The First Law of
Thermodynamics
 The foundation of the law of the
conservation of energy
 determination of the heat equivalence of
work
 Joule experiment
 Discription: Whenever a system
undergoes a cyclical process, the net
quantity of work produced in the
surroundings is proportional to the net
quantity of heat withdraw from the
surroundings, and the constant of
proportionality depends only on the units
in which work and heat are expressed.
MATHEMATIC EXPRESSION:
6.3 Quasi-Static Process and
Reversible Process
 Process undergoes so slowly that we can
think that the process is static;
 States and energy can be completely
recovered------reversible process .
6.4 Expression to Work
WORK
Volume work
Surface work
Electrical work
Magnetic work
Universal work
EXPRESSION
V2
A    pdV
dA   pdV
dA  ds
V1
dA  V E  d P
dA   0V H  d M
dA  Yi dyi
i
6.5 Heat Capacity and
Enthalpy
 1.constant-volume heat capacity and
specific heat, mole heat capacity:
 2.constant-pressure heat capacity and
specific heat, mole heat capacity:
 Enthalpy:
H  U  pV
 3.The relationship between Cv and Cp:
6.6 Internal Energy of Gas
 1. Joule experiment
 Adiabatic, free expansion Q=0, A=0
 No temperature change DT=0
 2. Analyze to Joule experiment :
6.7 Thermodynamic Processes
of the Ideal Gas
 1.Isometric Process, V=C
 2.Isobaric Process, P=C
 3.Isothermal Process, T=C
 4.Adiabatic Process, Q=0
 5.Polytropic Process
The graph of these processes:
p
Isobaric
Isometric
Isothermal
adiabatic
V
The main formula of these processes:
EQUATION
w
Q
U
V C
Cm,V (Tf  Ti ) Cm,V (Tf  Ti )
0
1 or p  C '
T
 p (V f  Vi )
pC
or
V

Cm, p (T f  Ti ) Cm,V (Tf  Ti )
'
2 or
 C  R(T f  Ti )
T
3 pV  C
 piVi ln V f / Vi
or
 RTi ln V f / Vi
A
0
C
Cm,V
Cm, p

EQUATION
w
Q
1
( p f V f  piVi )
 1
0
U
C
pV   C1
4
V  1T  C 2
p 1 T   C 3
Cm,V (Tf  Ti )
0
pV n  C1
5
V n 1T  C 2
p n 1 T n  C 3
1
Cm,n (T f  Ti )
  n
( p f V f  piVi )
C

C



C
(
T

T
)
m
,
n
m
,
V
m,V
f
i
n 1
1

n


(n  1)
6.7 Cycle Process
 1.Cycle process and its efficiency:
 2.Heat engine cycle:
 3.Refrigerator cycle:
4.Carnot cycle
p
:
a
b
T1
d
c
T2
V
 The efficiency of the Carnot cycle:
 Refrigeration-efficiency in Carnot cycle:
 Heat engine-efficiency in Carnot cycle:
T1
T1
Q1
Q1
A
A
Q2
T2
Q2
T2