An isothermal process keeps temperature constant by changing both pressure and volume simultaneously and oppositely, according to Boyle's law. An isobaric process keeps pressure constant by adding heat which increases the gas's internal energy and does work as its volume changes. An isovolumetric or isochoric process keeps volume constant, so no work is done and internal energy changes solely from heat. An adiabatic process is fully insulated so no heat enters or leaves; nothing is constant and internal energy changes result only from work done.

1. Thermodynamic Processes - Isothermal
To keep the temperature constant both
the pressure and volume change to
compensate.
(Volume goes up, pressure goes down)
i.e. BOYLES’ LAW
P
V
0
2
1
Isotherm
Isothermal T1 = T2 (Constant Temperature)
V1 V2
T1 = T2
Q
-W
0

T 0


 U


V
Since
By
W
Q
U 


By
W
Q 

0
By
W
Q 
Net
Work
Done

2. Thermodynamic Processes - Isobaric
Heat is added to the gas which
increases the Internal Energy (U).
Work is done by the gas as it changes
in volume.
The path of an isobaric process is a
horizontal line called an isobar.
0
2
1
V1 V2
Isobar
T1
T2
T2>T1
Q
-W
Isobaric P1 = P2 (Constant Pressure)
By
W
Q
U 


P
V
Net Work
Done

3. Thermodynamic Processes – Isovolumetric
(Isochoric)
0
2
1
V1= V2
Isomet
T1
T2
T2>T1
P
V
Isovolumetric V1 = V2 (Constant Volume)
Q W = 0
0

V
Since
By
W
Q
U 


0


 Q
U
Q
U 


4. Thermodynamic Processes - Adiabatic
ADIABATIC- GREEK
(adiabatos- "impassable")
In other words, NO HEAT can leave
or enter the system, it is fully
insulated.
0 V1 V2
P
V
Adiabatic = Nothing is Constant
T1
T2
T1>T2
2
1 Adiabat
Q = 0
-W
0

Q
Since
By
W
Q
U 


By
W
U 

 0
By
W
U 



5. In Summary
0
P
V
(b)
(a)
(c)
(d)
Label Process Important Points Gas Law
a Isothermal Constant T, ΔU = Q , Q = WBy Boyles Law
b Isovolumetric (isochoric) Constant V, W = 0, ΔU = Q Charles Law
c Isobaric Constant P, ΔU = Q - WBy Pressure Law
d Adiabatic Nothing is Constant, Q = 0, ΔU = -WBy Combined Gas Law
Isobaric
Isothermal
Isochoric
Adiabatic