100 Fun Facts About Thermodynamics

Why does water boil cooler on Everest?

Lower pressure: the summit air presses down with only about a third of its sea-level force, so water boils at about 70 °C and food takes far longer to cook.

Which way does heat never flow on its own?

From a colder body to a hotter one: heat makes that trip only when work forces it, which is why a refrigerator has to be plugged in.

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

The calorie comes from calor, Latin for heat; confusingly, the 'Calories' on food labels are kilocalories, each enough to warm a whole kilogram of water by one degree.

What is absolute zero on the Celsius scale?

−273.15 °C is the bottom of the scale, yet matter would not be perfectly still there: quantum mechanics leaves atoms a residual zero-point motion.

Which temperature scale is defined with absolute zero as 0?

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

Which English physicist used a falling weight to spin a paddle wheel in water and measure heat's mechanical equivalent?

James Joule found the churned water warmed by a fixed amount for each unit of work done, evidence that heat is a form of energy, and the SI unit of energy now bears his name.

Which physicist coined the word 'entropy' in 1865?

Rudolf Clausius built the word from the Greek for 'transformation' and deliberately made it resemble 'energy', because he saw the two quantities as close relatives.

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

−40 is the one point where the scales cross: a Fahrenheit degree is only five-ninths the size of a Celsius degree, so its 32-degree head start at freezing has run out by then.

Which practical problem drove the early development of thermodynamics?

Steam engines were powering British industry long before anyone understood the physics behind them, and Sadi Carnot's 1824 book set out to supply the missing theory.

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

Otto von Guericke, the mayor of Magdeburg, went on to pump the air from two joined copper hemispheres and show that teams of horses could not pull them apart.

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

Pressure and volume: halve a trapped gas's space and its pressure doubles, a rule Boyle published in 1662 after years at an air pump designed by his assistant, Robert Hooke.

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

Pressure cooker: Papin called it an 'engine for softening bones', and to keep the sealed pot from bursting he fitted it with the first safety valve.

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

Joseph Black noticed that melting ice soaks up heat without getting any warmer, and reasoned that the heat had become hidden, or 'latent', inside the water.

Which James Watt innovation slashed the Newcomen engine's appetite for fuel?

The external condenser came to Watt on a walk across Glasgow Green in 1765: condensing the steam in a separate vessel let the cylinder stay hot instead of being chilled on every stroke.

Thomas Newcomen's 'atmospheric engine', the workhorse of the early 1700s, was used mainly for what job?

Pumping water out of mines was almost its only use, and it burned fuel so wastefully that curing its appetite became James Watt's great project.

Which law did the 1850 paper 'On the Moving Force of Heat' first set out?

The second law emerged as the paper kept Carnot's insight about engines while rejecting the old belief that heat is a fluid that can never be used up.

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

Josiah Willard Gibbs published it in a little-read Connecticut journal in dense mathematics, so years passed before chemists grasped that it had founded a new branch of their science.

Which engine ignites its fuel by compression heating alone, with no spark plug?

The diesel engine compresses air fifteen-fold or more, which heats it past the fuel's ignition point, so the fuel burns as soon as it is injected; Rudolf Diesel patented the cycle in the 1890s.

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

Adiabatic: with no heat getting in or out, any work done on a gas goes straight into its internal energy, which is why air squeezed quickly grows hot.

What stays constant during an isobaric process?

Pressure: 'isobaric' joins the Greek for 'equal' and 'weight', and a gas heated under a freely sliding piston shows it, swelling in size rather than pushing any harder.

What is held constant in an isochoric process?

Volume stays fixed, so the gas can do no work by expanding and all the heat added goes into its internal energy, as when a sealed tin can is put on a fire.

Which thermodynamic quantity is written with the symbol H?

Enthalpy, from the Greek for 'to warm in', only got its name in the early 20th century; before that, the same quantity went by the plain label 'heat content'.

The zeroth law says two bodies each in thermal equilibrium with a third must share what with each other?

The same temperature: plain as it sounds, this is what lets a thermometer work, since its reading is only its own temperature once it has settled into balance with whatever it touches.

Why is the zeroth law called 'zeroth'?

It was added after the others: the name dates from the 1930s, when the other three laws were long established, and because it logically comes before them it was slotted in at zero.

What does the third law of thermodynamics say happens as a system nears absolute zero?

Entropy reaches a minimum, and for a flawless crystal that minimum is exactly zero, which hands chemists a fixed starting line for measuring the absolute entropy of any substance.

Which gas law says that a gas expands in direct proportion to its absolute temperature?

Charles's law honours Jacques Charles, who worked it out in the 1780s but never published; Joseph Gay-Lussac verified it, put it in print in 1802 and gave him the credit.

The 1959 lecture 'The Two Cultures' likened not knowing a famous law of thermodynamics to never having read whom?

Shakespeare: the speaker, C. P. Snow, said he had asked highly educated company to describe the law, the one about entropy, and got a response that was 'cold' and 'negative', his proof that arts and sciences no longer talked.

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

Spontaneous: the sign is the whole test, so even a reaction that soaks up heat will run on its own if it is hot enough for the entropy gained to outweigh the cost.

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

Ludwig Boltzmann has the resulting formula, S = k log W, carved on his tombstone, even though he never wrote it down in that form himself: Max Planck did.

Which gas did Heike Kamerlingh Onnes turn liquid in 1908, making his Leiden lab the coldest spot on Earth?

Helium turns liquid only about four degrees above absolute zero, and three years later that extreme cold let Onnes discover superconductivity, electric current flowing with no resistance.

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

Claude Shannon's paper, written at Bell Labs, also put the word 'bit' into print and showed that adding extra bits to a message lets transmission errors be corrected.

Who extended entropy into quantum mechanics using the density matrix?

John von Neumann, whose 1932 book gave quantum mechanics its rigorous framework, created what is now the yardstick of quantum information: the measure in which qubits are counted.

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

Time: the microscopic laws of motion work equally well run backwards, so the steady rise of entropy is what physicists point to when asked why the past differs from the future.

What is the only publication Carnot produced in his lifetime?

Reflections on the Motive Power of Fire founded a science yet was neglected for years: it drew a glowing review in 1824, then was little read until after its author's death.

Sadi Carnot was named after a medieval poet from which country?

Persia: he was named for Sa'di of Shiraz, a medieval poet and philosopher, by his father Lazare, then one of the five Directors governing revolutionary France.

Which disease killed Sadi Carnot at 36 during an 1832 Paris epidemic?

Cholera found him already weakened: a serious illness earlier that year had left him barely recovered when it struck him down in August.

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

Émile Clapeyron recast Carnot's wordy argument as equations and graphs, drawing the engine cycle as a closed loop on a chart, and that version is the one later physicists built on.

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

An upper limit on efficiency that depends only on the two temperatures the engine works between: no design or working fluid, however clever, can beat it.

What are the four stages of a Carnot cycle?

Two isothermal and two adiabatic stages, every one of them perfectly reversible, which is why no real engine quite manages the cycle: every real process creates some entropy.

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

James Clerk Maxwell first sketched it in an 1867 letter to a friend, to argue that the law of rising entropy is only statistical: overwhelmingly likely, not strictly certain.

In 1798 Count Rumford brought water to the boil using only the friction from boring which object?

A cannon barrel: grinding at it with a blunt borer boiled the water in about two and a half hours, and since the heat never ran out, Rumford argued that heat must be motion, not a fluid.

Who argued in 1929 that the famous 'demon' of physics must spend energy to measure molecules?

Leo Szilard pictured a box holding a single molecule and argued that the demon could only win by first gathering information about it, linking entropy to knowledge.

In the famous 'demon' thought experiment, what does the demon sort between two gas chambers?

Fast and slow molecules: by letting only the quick ones through one way, the demon would make one chamber hot and the other cold without doing any work, which is the trouble.

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

The Big Chill, also called the Big Freeze, is a universe at maximum entropy: energy spread so evenly that no differences in warmth remain to drive any process at all.

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

Lord Kelvin's 1852 paper on nature's 'universal tendency' to dissipate energy concluded that the Earth must, sooner or later, become unfit for human habitation.

Which physicist showed in 1974 that black holes are not entirely black but glow with faint heat radiation?

Stephen Hawking's result overturned the 'obvious' view that a black hole must sit at absolute zero, and it means a small enough hole would eventually evaporate away entirely.

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

The first law is conservation of energy in thermodynamic dress: energy can change form but can never be created, so no machine can pay out more work than it takes in.

The 12th-century Indian mathematician Bhaskara designed what type of perpetual motion device?

An overbalanced wheel: it carried mercury, which was supposed to flow so that one side always stayed heavier and the wheel never stopped turning.

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

A working model: the examiners' manual says a model 'is not ordinarily required', with the single stated exception of cases involving perpetual motion.

Which state of matter did ultracold rubidium form in 1995?

A Bose–Einstein condensate was predicted by Einstein in the 1920s, yet seventy years passed before anyone could make one; the feat won the 2001 Nobel Prize in Physics.

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.