1. Internal Energy and the First Law of Thermodynamics
Prof. Marlon Flores Sacedon
Department of Mathematics and Physics
College of Arts and Sciences
Visayas State University, Visca
Baybay City, Leyte, Phiippines

2. Internal Energy (U)
What is Internal Energy?
Internal Energy of a system is the sum of kinetic energies of all of its constituent particles, plus the sum of all the potential energies of interaction among these particles.
Where:
= change in internal energy
U1 = initial internal energy
U2 = final internal energy

3. The First Law of Thermodynamics
System
Surroundings
(environment)
Q = 150J
W = 100J
= Q-W
= 150J – 100J = +50 J
System
Surroundings
(environment)
Q = -150J
W = -100J
Where:
= change in internal energy (J)
W = work done (J)
Q = heat quantity (J)
= Q-W
= -150J – (-100J) = -50 J
System
Surroundings
(environment)
Q = 150J
W = 150J
= Q-W = 0

4. Human daily cyclic thermodynamic process

5. The First Law of Thermodynamics
Ex. A gas in a cylinder is held at a constant pressure of 2.30x105 Pa and is cooled and compressed from 1.70 m3 to 1.20 m3. The internal energy of the gas decreases by 1.40x105 J. a) Find the work done by the gas. b) Find the absolute value of the heat flow into or out of the gas, and state the direction of heat flow. c) Does it matter whether or not the gas is ideal?
(Ans. a) -1.15x105 b) 2.55x105J, out of gas, c) no

6. EXAMPLE: The pV-diagram of Fig. shows a series of thermodynamic
processes. In process ab, 150 J of heat is added to the system; in process bd, 600 J of heat is added. Find (a) the internal energy change in process ab; (b) the internal energy change in process abd (shown in light blue); and (c) the total heat added in process acd (shown in dark blue).

7. ASSIGNMENT

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12. eNd