Chapter 16: Thermodynamics

Internal Energy (U)

The sum of the particle kinetic and potential energies of a substance.

Thermal Equilibrium

The state where there is no net thermal energy flow between two objects at the same temperature.

Zeroth Law of Thermodynamics

If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

First Law of Thermodynamics

Energy is conserved in all natural processes; energy can neither be created nor destroyed, only transferred or transformed.

Key Principles

• Thermal energy flows from hot objects to cold objects until equilibrium is reached.
• Work (W) and heat (Q) relate to internal energy changes (ΔU): $Q=\mathrm{\Delta U}+W$

Example 16-1: Change in Internal Energy

A system is heated by 755 J of thermal energy and does 415 J of work, while losing 85 J to its surroundings. What is the change in internal energy (ΔU)?

• Given: Q_in = 755 J, W = 415 J, Q_out = -85 J
• Q = Q_in + Q_out = 755 J + (-85 J) = 670 J
• ΔU = Q - W = 670 J - 415 J = 255 J
• Answer: ΔU = 255 J

Historical Development

• The first steam engine was developed in the first century AD (aeolipile).
• James Watt’s steam engine marked a significant advancement in industrial applications.

Questions for Students

1. Define internal energy and explain how it relates to temperature.
2. State the Zeroth Law of Thermodynamics and provide an example of its application.
3. Write the formula for the First Law of Thermodynamics and explain each term.
4. Calculate the change in internal energy if a system absorbs 500 J of heat and does 200 J of work.
5. Discuss the historical significance of James Watt’s steam engine.