PART V KNOWLEDGE STRUCTURE
Thermodynamics

Key Findings

What are the overarching findings of Part V?

Thermodynamics is an expanded view of systems and energy.

A system exchanges energy with its environment via both work and heat. These are energy transfers.
In a heat engine, heat energy is transformed into useful work when a system follows a cyclical process.
Some processes are irreversible. A reversible Carnot engine is a heat engine with the maximum possible efficiency.
Many macroscopic thermal properties of materials can be understood in terms of the motions of atoms and molecules.

What laws of physics govern thermodynamics?

First law of thermodynamics	Energy is conserved: $Δ E_{th} = W + Q$ .
Second law of thermodynamics	Heat is not spontaneously transferred from a colder object to a hotter object: $Δ S \geq 0$ .
Ideal-gas law	$p V = n R T or p V = N k_{B} T$
Equipartition theorem	The energy stored in each degree of freedom is $\frac{1}{2} N k_{B} T or \frac{1}{2} n R T$ .

What are the most important models of Part V?

Work and heat are energies transferred between the system and the environment.
- Work is a mechanical interaction.
- Heat is a thermal interaction.
Transferring energy changes the system’s thermal energy as given by the first law: $Δ E_{th} = W + Q$ .

Full Alternative Text

For low densities and temperatures not too close to the condensation point, all gases, regardless of composition, obey the ideal-gas law with the same value of the gas constant R.

A perfectly reversible heat engine has the maximum possible efficiency of any heat engine operating between $T_{H} and T_{C}$ .
The efficiency depends only on the reservoir temperatures, not on any details of the engine: $η_{Carnot} = 1 - T_{C} / T_{H}$ .

What are the most important tools introduced in Part V?

pV diagrams show

Four fundamental gas processes

Work in gas processes

The work done on a gas is

$\begin{matrix} W & = & - \int_{V_{i}}^{V_{f}} p d V \\ = & - area under the p V curve \end{matrix}$
For a closed cycle, the work done by a gas is $W_{s} = area enclosed$ .

Heat and thermal energy

Heat is energy transferred in a thermal process when there is a temperature difference.
Thermal energy is the microscopic energy of moving atoms.
Heat, thermal energy, and temperature are related but not the same.

Heat is transferred by

Heating and cooling

The heat energy needed for a temperature change is $Q = m c Δ T or$ $Q = n C Δ T$ .
For thermally isolated systems

$Q_{net} = Q_{1} + Q_{2} + \dots = 0$

Heat engines and refrigerators

Heat engines and refrigerators require both a hot reservoir and a cold reservoir.

A heat engine transforms heat energy from a hot reservoir into work while exhausting energy to the cold reservoir.

Full Alternative Text
A refrigerator uses external work to “pump” heat energy from a cold reservoir to the hot reservoir.
A Carnot engine is the best possible engine or refrigerator.

Full Alternative Text