1
First Law of Thermodynamics
Two closed thermodynamic cycles for an
ideal gas
are depicted on the pV diagram.
Imagine processing the gas clockwise through Cycle
1 once.
Determine whether the change in internal
energy of the gas in the entire cycle is positive,
negative, or zero.
•
Δ
U
1clockwise
= 0
internal energy only depends on
initial and final states
Imagine processing the gas clockwise through Cycle
1.
Determine whether the work done on the gas in
the entire cycle is positive, negative, or zero.
Two closed thermodynamic cycles
•W
1clockwise
< 0
negative to the right, positive to the left, zero along
the vertical sides (isochoric). W =  area of rectangle.
Imagine processing the gas clockwise through Cycle 1.
Determine
whether the heat energy transferred to the gas in the entire cycle
is positive, negative, or zero.
Q
1clockwise
> 0
positive because W is negative and
Δ
U = W + Q = 0
Demo:steam engine
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
2
A cylinder with initial volume V contains a
sample of gas at pressure p. The gas is
heated in such a way that its pressure is
directly proportional to its volume. After the
gas reaches the volume 3V and pressure 3p,
it is cooled isobarically to its original volume
V. The gas is then cooled isochorically until it
returns to the original volume and pressure.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '09
 hoffman
 Thermodynamics, Law of Thermodynamics

Click to edit the document details