2. 0th Law of Thermodynamics
Consider 3 objects and their temperatures: T1 T2 T3
If T1 = T2 and T2 = T3
then T1 = T3

3. U W Q Walls can be either: Diathermal - heat can flow through
Surroundings
System U W Q
Walls can be either:
Diathermal - heat can flow through
or Adiabatic – heat can’t flow through
Car engine
Q W
Rub hands together
W Q

4. The internal energy of an ideal gas depends only on its temperature
The internal energy of an ideal gas depends only on its temperature. Therefore, the change in internal energy of a fixed amount of ideal gas (n moles) is given by:
Units: Joules (J) R = 8.31 J/mol K

5. 1st Law of Thermodynamics
The total increase in the internal energy of a system is equal to the ‘sum’ of the work done on the system or by the system and the heat added to or removed from the system.
(Conservation of Energy!)
+ve Q = system GAINS heat (ΔU↑)
-ve Q = system LOSES heat (ΔU↓)
-ve W=work done BY system (ΔU↓)
+ve W=work done ON system (ΔU ↑)

6. Pressure, Volume ,Temperature & Work
In Thermodynamics we talk about the state of the system:
Pressure, Volume ,Temperature & Work
Work Done on a Gas F
W = F Dx
DV = A Dx
W= PA Dx
W = -P DV Dx
Area
+ve W=work done ON system (ΔU↑)
COMPRESSION OF GAS DV
-ve W=work done BY system (ΔU↓)
EXPANSION OF GAS

8. Example: A gas is compressed from 1. 5 m3 to 1
Example: A gas is compressed from 1.5 m3 to 1.0 m3 under a constant pressure of 1.5 x 105 Pa while 3.0 x 105 J of heat is removed from the gas. What is the change in internal energy of the gas? Apply the first law.
Heat is removed (system losses)
Q = -3.0 x 105 J
Work is performed [W +ve] on the gas;
W = -pΔV = -(1.5 x 105Pa)(-0.5m3) = +0.75x 105J
The change in internal energy:
ΔU = -3.0 x 105 J x 105J = 2.25x 105J
System U W Q

10. During a thermodynamic process, 2,000 J of heat are removed from a gas while 600 J of work is done by the gas. What is the change in internal energy of the gas?
(A) +2,600 J
(B) 0
(C) -1,400 J
(D) -2,600 J
The internal energy of a sample of confined helium gas is increased by 300 J. If the net amount of work done on the sample by its surroundings was 240 J, how much heat was transferred between the gas and its environment?
(A) 60 J absorbed
(B) 540 J absorbed
(C) 60 J dissipated
(D) 540 J dissipated
A gas undergoes an expansion in which 300 J of energy is added to the gas by heating. The internal energy of the gas changes from 600 J to 700 J. The work done by the gas is:
(A) 1,300 J (B) 900 J (C) 200 J (D) 100 J

11. 1. If 600 J of heat is added to a system as 200 Joules of work is done on the system, what is the change in its internal energy?
2. If 300 J of heat is added to a system as 300 joules of work is done by the system, what is the change in its internal energy?
3. Three moles of monatomic, ideal gas are in a rigid container. If the temperature is raised by 200 K while 5000 Joules of heat is added, find the work done on the gas and its change in internal energy?
3 moles

12. A Thermal Process… P V Po Pf Vo Vf
4.An ideal gas expands to 10 times its original volume, maintaining a constant 440 K temperature. If the gas does 3.3 kJ of work on its surroundings, how much heat does it absorb? T P V Po Pf Vo Vf
In an isothermal process DU = 0
A Thermal Process…