📘 Heat: Thermodynamics

What you’ll learn

1. Heat, Temperature, and Thermal EquilibriumDistinguish heat from temperature and apply the zeroth law to systems in thermal contact.Heat is energy transferred due to temperature difference, not a stored fluid. The zeroth law establishes transitive thermal equilibrium and defines temperature empirically. These foundations allow consistent measurement scales and prepare for the first law.
2. The First Law and Internal EnergyState and apply the first law to closed systems with both heat and work exchanges.Internal energy is a state function fixed by the current state variables. Any process changes U only by the net energy crossing the boundary. Sign conventions for Q and W are fixed so that cyclic processes yield zero net change in U.
3. Work in Thermodynamic ProcessesCalculate expansion work for reversible and irreversible paths on a P-V diagram.Work is path-dependent and equals the integral of P dV. Reversible paths yield the maximum work for expansion and minimum work for compression. Graphical representation on indicator diagrams connects abstract integrals to measurable quantities.
4. Heat Capacity and EnthalpyRelate Cp and Cv through the first law and derive enthalpy for ideal gases.Enthalpy H = U + PV accounts for flow work in open systems. For ideal gases, both U and H depend only on temperature, so ΔH = nCpΔT. Experimental values of Cp and Cv reveal molecular degrees of freedom.
5. Phase Changes and Latent HeatApply latent-heat data to calculate energy requirements during isothermal phase transitions.Latent heat reflects the potential-energy change associated with breaking intermolecular bonds. On a P-V or T-S diagram the process appears as a horizontal line at constant pressure or temperature. Steam tables and property charts supply the numerical values used in engineering calculations.
6. The Second Law and EntropyDefine entropy as a state function and calculate ΔS for reversible and irreversible processes.Entropy increases quantify irreversibility and lost work potential. For reversible heat transfer, ΔS = ∫ dQrev/T. Irreversible processes generate entropy inside the system boundary, driving the universe toward thermodynamic equilibrium.
7. Heat Engines and Thermal EfficiencyApply the first and second laws to calculate thermal efficiency of heat engines.Efficiency η = Wnet/Qh = 1 – |Qc|/Qh. The second law requires |Qc| > 0 for any finite-temperature engine. Real plants fall short of ideal limits because of irreversibilities such as friction and finite temperature differences.
8. The Carnot CycleAnalyze the Carnot cycle on T-S and P-V diagrams and prove its maximum efficiency.All reversible engines operating between the same temperatures achieve the same efficiency. The T-S diagram shows that the enclosed area equals net work while the ratio of heat transfers fixes η. Any irreversibility reduces the enclosed area and therefore efficiency.
9. Refrigerators and Heat PumpsDerive coefficients of performance for refrigeration and heat-pump cycles.COPR = Qc/Wnet and COPHP = Qh/Wnet. Both exceed unity because the device moves existing thermal energy rather than creating it. The reversed Carnot cycle sets the theoretical upper bound on these coefficients.
10. Kinetic Theory of HeatConnect molecular kinetic energy to temperature and derive pressure from momentum transfer.Pressure arises from the rate of molecular collisions with container walls. Equipartition assigns 1/2 kT per quadratic degree of freedom, yielding Cv = 3/2 R for monatomic gases. This statistical foundation explains why temperature measures average kinetic energy.
11. Irreversibility and Entropy GenerationCalculate entropy generation for mixing, throttling, and heat-transfer processes.Entropy generation is always positive inside real boundaries. Mixing, unrestrained expansion, and finite ΔT heat transfer are classic sources. Quantifying σgen identifies the largest irreversibilities for engineering improvement.
12. Applications and Measurement StandardsLink thermodynamic theory to calibrated instruments and property databases used in engineering practice.Standard reference data allow engineers to predict performance before building devices. Real-time sensors and property tables convert the abstract laws into quantitative design tools. The course therefore ends by returning heat and temperature to measurable laboratory quantities.

Questions this course answers

Grounded in trusted sources

• National Institute of Standards and Technology
• U.S. Department of Energy
• NASA
• OpenStax University Physics, Heat and Heat Transfer Methods, https://openstax.org/books/university-physics-volume-2/pages/1-introduction
• PhET, Energy Forms and Changes, https://phet.colorado.edu/
• Khan Academy, Specific heat and calorimetry, https://www.khanacademy.org/science/physics
• NASA, Heat transfer education resources, https://www.nasa.gov/

Every Wunder lesson is built from real, reputable sources — never invented.

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