THM-01

First law of thermodynamics

ΔU = Q − W, heat in minus work out (IUPAC).

Reading speed

LawsClausius / Joule

Governing equation

\Delta U = Q - W

$Q \in \left[-500, 500\right]$

where

Q: Heat in (kJ)
W: Work out (kJ)
\Delta U: Internal-energy change (kJ)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

\Delta U = Q - W

$Q \in \left[-500, 500\right]$

$Q = -500$ $\Delta U = -530$

Along the curve

②

Domain of the variable — blue

Q_{\min} = -500,\quad Q_{\max} = 500

$Q \in \left[-500, 500\right]$

$Q = -500$ $Q = -500$

Along the curve

③

Response curve — green

\Delta U = Q - W

$Q \in \left[-500, 500\right]$

$Q = -500$ $\Delta U = -530$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}\Delta U}{\mathrm{d}Q}

$Q \in \left[-500, 500\right]$

$Q = -493.7$ $\Delta U^{\prime} = 1$

Along the curve

Lecture brief

Historical brief

Carnot (1824), Clausius entropy, the first law and later van der Waals and Gibbs potentials turned heat into a state science. The sheets compute work, efficiency and vapour pressure. This sheet (THM-01 — First law of thermodynamics) is the form associated with Clausius / Joule. Working symbols: $Q$ , $W$ $\rightarrow$ $\Delta U$ . Energy is conserved: the increase of internal energy of a closed system equals heat added minus work performed by the system.

Purpose

Purpose: compute

\Delta U

from

Q

W

in Thermodynamics via

\Delta U = Q - W

ΔU = Q − W, heat in minus work out (IUPAC). Use it when a real thermodynamics question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

Q = 80.000\,\mathrm{kJ}

W = 30.000\,\mathrm{kJ}

, the governing relation

\Delta U = Q - W

yields

\Delta U = 50.000\,\mathrm{kJ}

. Closed system, sign convention: Q in, W out. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Heat in Q80 kJWork out W30 kJ

Outputs

Internal-energy change \Delta U50.000 kJ

Reading speed

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Narration of this film

Closed system, sign convention: Q in, W out.

Energy is conserved: the increase of internal energy of a closed system equals heat added minus work performed by the system.

Reading speed

Watch on YouTube