Thermodynamics
Thermodynamics
• The study of processes in which energy is
t
transferred
f
d as heat
h t and
d as work.
k
• Thermodynamics system
– Object or set of objects we wish to consider
(everything else is environment)
– Could be closed or open system
1
1st Law of Thermodynamics
• The change in internal energy of a closed
system
t
will
ill b
be equall tto th
the h
heatt added
dd d tto
the system minus the work done by the
system
ΔU = ΔQ − ΔW
internal
energy
work
heat
ΔQ = ΔU + ΔW
1st Law
• This law is really just a statement of
conservation
ti off energy.
• Q and W represent energy transferred into
and out of the system.
2
Notes:
•
•
•
•
Work done on the system is negative
Work done by the system is positive
Heat added to the system is positive
Heat lost by the system is negative
Thermodynamic Processes
3
Isothermal Process
• Temperature is
constant
t t
• Internal energy does
not change
Q = ΔU + W
ΔU = 0
Q =W
4
Adiabatic Process
• No heat is transferred
• Well insulated container, quick
compression or expansion
Q = ΔU + W
Q=0
ΔU = −W
5
Isobaric Process
• Pressure is constant
• Work is done:
W = Fd
P=
F
A
W = PAd
W = PΔV
6
Isochoric
(Isovolumetric)
• No
N work
k iis d
done
• Volume is constant
7
Work Done by a Gas
• Consider the following thermodynamic cycle
8
Work done by a gas as it expands
Work done on a gas as it is compressed
9
Net work done by the gas
10