100 Fun Facts About Thermodynamics

How many laws of thermodynamics are there?

The zeroth law was added after the other three were already numbered, because renumbering them was impractical.

Which way does heat never flow on its own, according to a classic statement of the laws?

That everyday observation is one traditional way of stating the second law.

Which law of thermodynamics expresses the conservation of energy?

Energy can be transformed from one form to another but cannot be created or destroyed.

What is absolute zero on the Celsius scale?

The same point is −459.67 °F and 0 on both the Kelvin and Rankine scales.

Which temperature scale is defined with absolute zero as 0?

The Rankine scale also starts at absolute zero but uses Fahrenheit-sized degrees.

Who is known as the 'father of thermodynamics'?

His 1824 Reflections on the Motive Power of Fire was the only book he ever published.

Which physicist coined the word 'entropy' in 1865?

He chose a Greek word for transformation and deliberately made it sound like 'energy'.

The word 'entropy' was coined from a Greek word meaning what?

Clausius first called it Verwandlungsinhalt, transformation-content, before settling on the Greek-derived name.

Which practical problem drove the early development of thermodynamics?

Carnot's 1824 analysis of engines was later built upon by Kelvin and Clausius.

Who built the world's first vacuum pump in 1650?

He wanted to disprove Aristotle's claim that nature abhors a vacuum, and did so with his Magdeburg hemispheres.

Boyle's Law says which two gas properties are inversely proportional?

Boyle and Hooke noticed the correlation using an air pump built in 1656.

Denis Papin's 1679 'steam digester' was essentially an early what?

Watching its release valve bob up and down gave him the idea of a piston-and-cylinder engine.

Who developed the concepts of heat capacity and latent heat at the University of Glasgow?

James Watt was the university's instrument maker at the time and experimented alongside him.

Which innovation by James Watt greatly improved steam engine efficiency?

Watt conceived it while employed as an instrument maker at Glasgow alongside Joseph Black.

Who wrote the first thermodynamics textbook in 1859?

Originally trained as a physicist, he was a professor of civil and mechanical engineering at Glasgow.

What did Clausius's 1850 paper 'On the Moving Force of Heat' first state?

It earned him the title of one of the founding fathers of thermodynamics.

Which American published 'On the Equilibrium of Heterogeneous Substances' in the 1870s?

His graphical methods showed whether a process, including a chemical reaction, would occur spontaneously.

Who presented a purely mathematical, axiomatic thermodynamics in 1909?

His approach, using adiabatic accessibility, is often called geometrical thermodynamics.

A process that occurs with no heat exchange is called what?

A reversible adiabatic process also keeps entropy constant and is called isentropic.

What stays constant during an isobaric process?

Isochoric processes, by contrast, hold volume fixed.

What is held constant in an isochoric process?

It is also called an isometric or isovolumetric process.

An isenthalpic process occurs at constant what?

Isentropic, a reversible adiabatic process, is the one that holds entropy constant.

Per the zeroth law, if A and B are each at the same temperature as C, then what?

The law is tacitly assumed in every temperature measurement and justifies building thermometers.

Why is the zeroth law called 'zeroth'?

The first, second and third laws were already accepted, and renumbering them was impractical.

What does the third law say happens as temperature approaches absolute zero?

A consequence is that absolute zero cannot be reached in a finite number of steps.

Which pair are the 'thermal' conjugate variables in thermodynamics?

Pressure-volume are the mechanical pair, and chemical potential-particle number the material pair.

Which two potentials give the work available at fixed T and V, or fixed T and p?

They cannot be measured directly in a lab but can be computed from molecular thermodynamics.

A negative change in Gibbs free energy indicates what kind of process?

The relation is ΔG = ΔH − TΔS, with T in kelvin.

Who gave entropy its statistical meaning as a count of microscopic arrangements?

His logarithmic law carries a proportionality constant, now one of the SI's defining constants.

In what year did Boltzmann define entropy via the logarithm of the number of microstates?

The Boltzmann constant is the proportionality factor in that definition.

Who devised the information-theory version of entropy in 1948?

He was studying the size of information in a transmitted message.

Who extended entropy into quantum mechanics using the density matrix?

His Mathematische Grundlagen der Quantenmechanik built the rigorous framework for quantum measurement.

Entropy is said to imply an 'arrow of' what?

It is the only quantity in the physical sciences that seems to point in a particular direction of progress.

What is the only publication Carnot produced in his lifetime?

It attracted little attention until Émile Clapeyron's 1834 commentary reached Kelvin and Clausius.

Carnot was named after a poet from which country?

His father Lazare chose the name of the 13th-century poet Sadi of Shiraz.

At what age did Carnot die, of cholera, in 1832?

He died in relative obscurity in a sanatorium at Ivry, south of Paris.

Which French engineer's 1834 commentary rescued Carnot's work from obscurity?

It brought the ideas to Lord Kelvin and Clausius, who built the absolute temperature scale and entropy on them.

What does Carnot's theorem provide for any classical heat engine?

A Carnot cycle is reversible; run backwards, it works as a refrigerator or heat pump.

What are the four stages of a Carnot cycle?

Real engines that follow this cycle are rare, but it fixes the best efficiency any engine can hope for.

Who proposed the 'demon' thought experiment that seems to defy the laws of thermodynamics?

Maxwell himself, a devout man, only ever called it a 'finite being'; Kelvin supplied the name in 1874.

Who first called Maxwell's 'finite being' a demon?

He meant the Greek sense of a daemon working in the background, not a malevolent spirit.

Who argued in 1929 that the demon's need to measure molecules costs energy?

The insight linked thermodynamics to information; Landauer later pinned the cost specifically on erasing information.

In which book did Maxwell present his demon to the public in 1872?

It had first appeared in a letter to Peter Guthrie Tait in December 1867.

The 'heat death of the universe' is also known by what nickname?

It describes a universe at maximum entropy, with no temperature differences left to do work.

Whose 1850s ideas on mechanical energy loss gave rise to the heat death hypothesis?

He extrapolated the first two laws to the universe as a whole and derived a paradox against an infinitely old cosmos.

Which French astronomer suggested in 1777 that all bodies in the universe cool off?

He corresponded with Voltaire about it, judging Venus still too hot for life and Mars already too cold.

A machine that produces work with no energy input would violate which law?

It would produce work with no energy input; the second kind would turn heat wholly into work instead.

Bhaskara's 12th-century perpetual motion design was what type of device?

The overbalanced wheel remains one of the most recurring ideas among would-be inventors.

Which 17th-century bishop listed three power sources for perpetual motion machines?

The Bishop of Chester named chemical extractions, magnetic virtues and gravity as early as 1670.

What record-low effective temperature, in picokelvin, was set in 2021?

It was achieved by matter-wave lensing of rubidium Bose-Einstein condensates.

Which phenomenon, named after a schoolboy, describes hot water sometimes freezing faster than cold?

The Mpemba effect is named after Erasto Mpemba, who noticed in a 1963 cookery class that his hot ice cream mixture froze before a cold one. Physicists dispute how reliably it can be reproduced.

Which Cambridge physicist predicted that black holes have a temperature and slowly radiate energy?

Stephen Hawking's 1974 prediction tied gravity to thermodynamics by treating a black hole as a warm, glowing body. Left alone, such a hole would keep losing mass until it evaporated.

Which effect makes the top of the Eiffel Tower lean up to 18 cm away from the sun?

Thermal expansion lengthens the metal on the side facing the sun, so the summit tilts toward the shade. Railways and bridges are built with expansion joints to cope with the same stretching.

At which reading do the Fahrenheit and Celsius thermometer scales show exactly the same number?

Only at −40° do the two scales agree, because they start from different zeros and use degrees of different sizes. Fahrenheit's own paper suggests he set his zero with a freezing brine of ice, water and salt.

What did zero mark on Anders Celsius's original thermometer scale, which was flipped after his death?

Water boiling sat at 0 and freezing at 100 on the thermometer Celsius calibrated. The scale was reversed in 1745, a year after he died, to give the familiar version.

Which classic desk toy is really a small heat engine, kept moving by water evaporating from one end?

The drinking bird dips because evaporation cools its felt-covered head, shifting the fluid sealed inside until it tips forward. It is sometimes mistaken for a perpetual motion device.

Which Scottish chemist invented the vacuum flask to store liquefied gases but never patented it?

James Dewar built his vacuum-jacketed vessel around 1892, then lost a court case against Thermos, the firm that turned his laboratory flask into a household product.

At room conditions, every diamond is very slowly turning into which more stable form of carbon?

Graphite is the stable form of carbon in everyday conditions, so diamond is only metastable. An energy barrier makes the change so slow that it would take millions to billions of years.

Which English brewer showed with a paddle wheel in a water barrel that mechanical work becomes heat?

James Joule managed his family's brewery, and while on honeymoon he arranged an attempt to compare the temperature at the top and bottom of a waterfall. The SI unit of energy carries his name.

By which process does dry ice turn straight from a solid into a gas, skipping the liquid stage?

Sublimation is all dry ice can do in open air, because carbon dioxide has no liquid state at normal atmospheric conditions. The solid turns to gas at −78.5 °C and leaves no residue.

Which Christopher Nolan thriller turns on bullets and people whose entropy has been "inverted"?

Tenet follows a spy tracing "inverted" munitions back to an arms dealer. Nolan had physicist Kip Thorne analyse his early ideas, while promising not to claim the science was real.

Which German engineer's engine ignites fuel by the heat of tightly squeezed air alone, with no spark plug?

Rudolf Diesel wanted an engine that wasted far less of its fuel's heat than the machines of his day. In 1913 he boarded a steamer from Antwerp to England and was never seen alive again.

Which unit was defined as the heat needed to warm a millilitre of water by one degree Celsius?

Calorie comes from the Latin calor, meaning heat. The Calorie on a food packet is the large kind, worth a thousand of the small calories that chemists and physicists use.

Which Massachusetts-born scientist, later a Bavarian count, decided heat is motion after watching cannon being bored?

Benjamin Thompson, better known as Count Rumford, found that the friction of boring cannon in Munich gave a seemingly inexhaustible supply of heat. He also created the city's Englischer Garten park.

Which gas law, named after a French balloonist, says a gas takes up more room the warmer it gets?

Charles's law honours Jacques Charles, who flew in the first crewed hydrogen balloon over Paris in 1783. He never published the rule himself; Gay-Lussac did, crediting Charles's old notes.

Instant cold packs turn chilly when ammonium nitrate dissolves in water, an example of which kind of process?

Endothermic processes absorb heat from their surroundings, which is why the pack cools as soon as its inner bag of water is squeezed open.

Until 2019 the SI unit of temperature was defined by which special state of water, found at 0.01 °C?

The triple point is the single condition at which a substance's solid, liquid and gas all coexist in balance. For water it sits a hundredth of a degree above the ordinary melting mark.

Coffee is often decaffeinated with carbon dioxide held in which state, neither clearly a liquid nor a gas?

Supercritical fluid carbon dioxide seeps through the beans like a gas yet dissolves caffeine like a liquid. Past a substance's critical point, separate liquid and gas phases no longer exist.

Which German physicist solved the puzzle of how hot objects glow by assuming energy comes in tiny packets?

Max Planck's packets, or quanta, founded quantum theory and won him the 1918 Nobel Prize in Physics. As a student he had been advised that physics was a nearly complete science.

Which American engineer designed the first modern air conditioner to tame humidity at a Brooklyn printing plant?

Willis Carrier drew up the system in 1902 because humid summer air made the printer's paper grow and shrink, so the coloured inks no longer lined up.

Which type of engine, patented by a clergyman in 1816, can run on any outside source of heat?

Stirling machines keep their working gas sealed inside and warm it from outside, so sunlight or a wood fire will drive one. Robert Stirling called his invention an air engine.

Which English ironmonger built the atmospheric engine that, from about 1712, pumped water out of flooded mines?

Thomas Newcomen sold tools to the mining trade, so he knew how badly the pits flooded. A Baptist lay preacher, he combined the ideas of two earlier inventors to build his pump.

Which Greek engineer of the first century described the aeolipile, a hollow ball spun round by jets of steam?

Hero of Alexandria's spinning ball is considered the first recorded steam turbine, yet it was never a practical source of power.

Which gas did Heike Kamerlingh Onnes turn into a liquid in 1908, just a few degrees above absolute zero?

Helium had to be chilled to about −269 °C before it would condense. Three years later Onnes used the liquid to discover superconductivity, the vanishing of electrical resistance.

Which random jiggling of pollen in water, explained by Einstein in 1905, is caused by collisions with unseen molecules?

Brownian motion is named after the botanist Robert Brown, who described it in 1827. Einstein's account served as convincing evidence that atoms and molecules exist, which Jean Perrin's experiments confirmed.

The absolute temperature of a gas is proportional to the average of which property of its randomly moving molecules?

Kinetic energy of the jostling molecules is what a thermometer really registers. Daniel Bernoulli proposed the idea in a 1738 book, but his theory was not immediately accepted.

Which author's story The Last Question has a giant computer asked, age after age, how to reverse entropy?

Isaac Asimov called it his favourite of his own short stories. The computer, Multivac, keeps replying that it has insufficient data for a meaningful answer.

Which home heating device delivers more warmth than the electricity it uses by drawing energy from outside air?

A heat pump only has to move warmth indoors rather than create it, so the work it needs is less than the heat it releases. That makes it more efficient than plain electric resistance heating.

Which thermodynamic cycle is the one most commonly found in car engines?

Otto is the name it carries because Nicolaus Otto was the first to build a working four-stroke engine. A Frenchman, Alphonse Beau de Rochas, had patented the idea earlier but never built one.

What does the US Patent Office require before it will grant a patent on a perpetual motion machine?

A working model is demanded for almost nothing else: perpetual motion is the stated exception to the rule that inventors need not show that a device operates. Applications are filed anyway, then most probably rejected.

In the equation ΔU = Q − W, where Q is heat added and W is work done, what does U denote?

Internal energy is everything stored inside a system, from the jiggling of its molecules to the chemical bonds between them. The equation is bookkeeping: heat in, minus work out, is what stays.

Which term do chemists use for a property that depends only on a system's present condition, not on how it got there?

State function is the label for quantities such as entropy, fixed by where a system is regardless of how it arrived. Heat and work are the opposite kind, depending on the path taken.

Temperature is which kind of property, one whose value stays the same when a sample is split in half?

Intensive properties such as density and hardness do not depend on how much material is measured. Mass is the reverse: cut the sample into two halves and it halves as well.

Which kind of system swaps neither matter nor energy with its surroundings, a condition never fully achieved?

Isolated is the strictest label, since a merely closed system can exchange energy while keeping its matter. Perfect isolation is an idealised notion, because in practice some transfer is always possible.

Which chemistry law, named after a Swiss-born Russian, says a reaction's total heat change ignores the route taken?

Hess's law lets chemists calculate the heat of a reaction they cannot measure directly, by adding up steps they can. Germain Hess, a chemist and physician, published it in 1840.

Which equation, usually written PV = nRT, do real gases obey only approximately, and best when thin and hot?

The ideal gas law combines several older gas rules in a single line. It pictures particles with no size and no pull on one another, which real gases resemble only at low density and high temperature.

Which German chemist won the 1920 Nobel Prize for the heat theorem that became the third law of thermodynamics?

Walther Nernst also invented an electric lamp and sold the patent for a million marks, wisely declining royalties shortly before tungsten bulbs took over.

Compared with anything at a positive temperature, a system at a negative absolute temperature is, surprisingly, what?

Hotter is the answer, because heat flows from a negative-temperature system into a positive one whenever they touch. Such states lie beyond infinite temperature, not below absolute zero.

Which phenomenon, named after a German doctor, makes water droplets skitter across a very hot pan?

The Leidenfrost effect leaves each drop hovering on a cushion of its own vapour rather than touching the metal, so it takes longer to evaporate than on a cooler pan.

Which part, invented by clockmaker John Harrison, curls as it warms and switches many thermostats on and off?

The bimetallic strip bonds two metals that respond differently to heat, which forces it to bend. Harrison devised it for his third sea clock, to keep it accurate as the temperature changed.

Which German ship's doctor returned from a voyage to Jakarta to declare that energy is neither created nor destroyed?

Julius von Mayer began thinking about heat after noticing that storm-whipped waves were warmer than a calm sea. His 1841 statement was largely ignored and others took the credit.

Which quantum physicist's book What Is Life? argued that living things survive by feeding on "negative entropy"?

Erwin Schrödinger based the book on public lectures he gave in wartime Dublin. Both discoverers of DNA's double helix later credited it as an inspiration for their early research.

Which glass bulb with black-and-white vanes spins in sunlight, driven by warmed gas and not by the push of light?

The Crookes radiometer would turn the other way if the push of light drove it, since the shiny faces reflect light and would recoil hardest. William Crookes invented it in 1873 during chemical research.

Which English potter was elected to the Royal Society for a device that measured the fierce heat inside kilns?

Josiah Wedgwood's pyrometer relied on the way clay contracts as it is fired, so the size of a test piece revealed how hot the kiln had been. He was elected in 1783.

Which American chemist, famous for electron-dot diagrams, introduced fugacity to describe how real gases behave?

Gilbert Lewis took the word from the Latin for 'to flee', picturing a gas's tendency to escape. He was nominated for the Nobel Prize in Chemistry 41 times and never won it.

At roughly which temperature is fresh water densest, the reading found year-round at the bottom of deep lakes?

4 °C water sinks beneath both warmer and colder layers, so a deep lake ices over from the top instead of freezing from the bottom up. Most liquids simply keep getting denser as they cool.

What dramatic name did Paul Ehrenfest give classical physics' prediction that a hot body radiates unlimited energy?

The ultraviolet catastrophe was the old theory's failure at short wavelengths, where it predicted infinite emission although it matched experiment at long ones. Ehrenfest coined the phrase in 1911.

Landauer's principle, proposed at IBM in 1961, sets a minimum heat cost on which basic computing operation?

Erasing a bit is logically irreversible, so the information that vanishes has to leave as a tiny amount of heat. The minimum cost rises with the temperature the hardware runs at.

Which temperature sensor, made by joining wires of two different metals, produces a voltage that changes with heat?

A thermocouple exploits an effect found in 1821, when Thomas Seebeck saw a compass needle swing beside a heated junction of two metals. He took it for a form of magnetism.

Which student of John Wheeler first proposed that a black hole's entropy is proportional to the area of its horizon?

Jacob Bekenstein made the suggestion in 1972, the year he completed his doctorate at Princeton. His link between horizon area and entropy launched the field of black hole thermodynamics.