First Law of Thermodynamics
Thermodynamic systems, internal energy, work done by expanding gas (W = ∫ P dV), First Law statement (ΔQ = ΔU + W), and isothermal, isobaric, isochoric, and adiabatic processes.
Marking a lesson complete represents finishing your study of the topic; it does not denote tested mastery.
Learning Objectives
- Apply First Law of Thermodynamics energy balance ΔQ = ΔU + W with consistent sign conventions.
- Interpret PV indicator diagrams and calculate work done as the area under the process curve.
- Compare isothermal (T = const, ΔU = 0) and adiabatic (ΔQ = 0, PV^γ = const) expansions.
Core Theory & Concepts
The First Law of Thermodynamics is the universal law of conservation of energy applied to thermodynamic systems. Heat added to a system either increases its internal energy or performs work on the surroundings.
First Law of Thermodynamics
ΔQ = ΔU + W, where ΔQ is heat supplied, ΔU is increase in internal energy, and W is work done by the system.
Work Done on PV Diagram
Work done equals the area under the process curve on a pressure-volume indicator diagram: W = ∫ P dV.
Common Misconceptions
A gas doing work in an expansion must always have heat supplied to it.
Syllabus Topic Outline
- 1Concept of internal energy U and state functions
- 2Work done during expansion: W = ∫ P dV (area under PV graph)
- 3First Law equation: ΔQ = ΔU + W
- 4Isothermal, isobaric, isochoric, and adiabatic processes