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

where

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

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

Watch on YouTube

Free library

Full library

Free PDF / open book

YouTube channels

00:0 / 00:08

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