the molecules of the system and the molecules of the environment exchange their thermal kinetic energies.
5. The relationship between work and heat stirring
3.The work done by system during equilibrium process
dW Fdl pSdl pdV
Work is process quantity
W V2 pdV p V1
FFFSSS
1
p dl
The value of the work equals the total area under the process curve of p~V diagram.
Heating
Work and heat have same effect for the system. Joule proved that 1 cal of heat causes the same temperature increment as that of 4.18 joule of work does. i.e. 1cal= 4.186 J
第一类永动机： E2 - E1= 0 （循环） Q = 0 （外界不供给能量） W > 0 (对外界作功)
“Heat” and “Work” can not be transformed without thermodynamic system.
Heat
system
Work
§7-3 Application of the First Law to isochoric, isobaric & isothermal Processes
V1 dV
2
V2 V
4. Heat ---- macroscopic displaying of thermal motions
Process quantity
Transfer heat ： one form of exchanging energy between system and its environment as the temperature difference.
working substance
Thermodynamic system
2. Internal energy
E ki pij
i
i, j
E(T ) M i RT Ideal gas Internal energy
2
state quantity Depends on T of the system only.
Thermodynamic system
its surroundings
Thermodynamic systems in engineering: Gas: such as air. Vapor: such as steam. Liquid: such as freon(氟利昂). Solid: such as semiconductor…….. They are also called as working substance
§7-2 The First Law of Thermodynamics
1. The first law …
Q E2 E1 W E W
Stipulation: Q: “+” the system absorbs heat from exterior
“－” the system gives out heat to exterior
1. Isochoric (Constant volume) process(V=Const.)
differential form： dQ dE dW
for the equilibrium process of ideal gas：
Q
M
i 2
R(T2
T1)
V2 pdV
V1
Mi
dQ RdT pdV
2
Other description of the FLT:
There is not any system(machine) that can do work forever without the supply of heat. Or It is impossible to make out the first kind of perpetual motion machine.
Note The FLT …can be used for any thermodynamic
procesቤተ መጻሕፍቲ ባይዱ of any thermodynamic system.
---Conservation law of energy including the heat phenomena and thermal motion.
E: “+”the internal energy of system increases
“－” the internal energy of system W:d“e+c”retahseessystem does work on exterior.
“－” exterior does work on the system.
Fundamentals of thermodynamics
Study what rules must follow when the macroscopic parameters of thermodynamic system change.
§7-1 Internal Energy Heat &Work
1. Two basic concepts: Thermodynamic system: is a system that can interact with its surroundings in at least two ways, one of which must be heat transfer. Surroundings(exterior): everything outside the system.