First Law: Internal Energy, Work & Heat

Module 2 · 2 of 8

🔥First Law: Internal Energy, Work & Heat

Energy is conserved — but the path matters

🔥

Energy is conserved — but the path matters

Heat and work are two ways of moving energy across a boundary. Their sum — the change in internal energy — depends only on the endpoints, but how much is heat versus work depends entirely on the path. Expansion work is the bridge from p–V diagrams to energy.

Difficulty

intro

Time

~35 min

Equations

Practice Qs

Learning Objectives

✓State the first law ΔU = q + w and the sign convention used
✓Compute expansion work for isothermal, adiabatic, isobaric and isochoric paths
✓Distinguish reversible (maximum) work from irreversible work
✓Explain why U and H are state functions while q and w are not
✓Connect qp to ΔH and qV to ΔU

Prerequisites

Ideal-gas lawIntegration of p dV (basic calculus)

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