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“Water boils at 100 degrees Celsius at a pressure of 1 atmosphere.”
The conclusion
Water's accepted normal boiling point is approximately 100°C at a pressure of 1 atmosphere. Modern temperature scales and precise measurements can produce values differing by a few hundredths of a degree, but that minor technical variation does not change the standard scientific statement.
Caveats
- The 100°C figure is a conventional rounded value; highly precise modern values can differ by a few hundredths of a degree.
- The statement assumes pure water in equilibrium, since dissolved substances can change its boiling point.
- Boiling temperature changes when atmospheric pressure differs from 1 atmosphere, including at higher altitudes.
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Sources
Ranked by source quality and relevance
The normal boiling point of water is 100°C (212°F) because this is the temperature at which the vapor pressure of water is 760mmHg, or 1atm (14.7psi).
Tboil | 373.17 ± 0.04 | K | [AVG](https://webbook.nist.gov/chemistry/site-cal.html#AVG) | N/A | Average of 7 values
Boiling is an extreme form of evaporation that occurs when the saturation vapor pressure is equal to the total atmospheric pressure.
The vapor pressure of water is 1 atm (101.325 kilopascals) at 100°C, the normal boiling point of water.
When a liquid reaches the temperature at which its vapor pressure equals one atmosphere, it has reached its _normal boiling point_. An _atmosphere_ is a unit of pressure that is equivalent to the air pressure at sea level. … At sea level, water boils at 212 degrees Fahrenheit(212°F) or 100 degrees [Celsius](https://www.ebsco.com/research-starters/science/celsius-and-kelvin-scales) (100°C).
It seems like one of those basic science facts: Water boils at 212 degrees Fahrenheit (100 degrees Celsius), right? Well, not always. It depends on where you’re doing the boiling.
At sea level, vapour pressure is equal to the atmospheric pressure at 100 ˚C, and so this is the temperature at which water boils.
There are two conventions regarding the _standard boiling point of water_: The _normal boiling point_ is commonly given as 100 [°C](https://en.wikipedia.org/wiki/Celsius "Celsius") (212 [°F](https://en.wikipedia.org/wiki/Fahrenheit "Fahrenheit")) (actually 99.97°C (211.9°F) following the thermodynamic definition of the Celsius scale based on the [kelvin](https://en.wikipedia.org/wiki/Celsius "Celsius")) at a pressure of 1atm (101.325kPa).
Equilibrium Diagrams of Water + NaCl or KCl + 2‑Methyl 2‑Propanol at the Boiling Temperature and 101.3 kPa
This “liquid-vapor” curve separates the liquid and gaseous regions of the phase diagram and provides the boiling point for water at any pressure. For example, at 1 atm, the boiling point is 100 °C.
All boiling points below are normal/atmospheric boiling points: they give the temperature at which the vapor pressure of the liquid is equal to atmospheric pressure at sea level, 1 atm. … - Boiling point of **water**: 100 °C / 212 °F
Use standard reference data or the phase diagram of water, which shows that at 1 atm pressure, pure water boils at 100 °C.
This “liquid-vapor” curve separates the liquid and gaseous regions of the phase diagram and provides the boiling point for water at any pressure. For example, at 1 atm, the boiling point is 100 °C.
For example, for water, the boiling point is 100 degrees Celsius at a pressure of 1 atm.
Pure water boils at 100 degrees Celsius at Standard Pressure (1 atm).
For example, the normal boiling point of water is 100 oC. … The normal boiling point is defined as the boiling point of a liquid at an external pressure of 1 atmosphere or 760 mm Hg.
A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. … | 760000 | 29.92 | 14.696 | 1013.3 | 0 | 0 | 0 | 100 | 212 |
Boiling point for water (1 atm ) : 100 C Celsius , 373.15 K Kelvin , 212 F Fahrenheit
Water boils at 212°F at sea level, but changes in elevation and atmospheric pressure alter that temperature. … Boiling Point Results 212.00°F / 100.00°C
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Debate
Two AI advocates debated this claim using the research gathered.
Argument for
An overwhelming consensus of authoritative, verified sources—including NIST (Source 2), ScienceDirect (Source 1), and McGraw Hill's AccessScience (Source 4)—confirms that water's vapor pressure equals 1 atm precisely at 100°C, the defining condition for the normal boiling point, with NIST's average of experimental measurements placing it at 373.17 K (99.97-100°C), effectively 100°C within standard rounding used universally in science and engineering. Across nineteen independent sources spanning academic journals (Source 3, Source 9), educational institutions (Source 10, Source 13, Source 14), and reference works (Source 8, Source 11, Source 16), this figure is consistently and independently corroborated, demonstrating that the claim reflects settled scientific fact rather than mere approximation.
The Proponent explicitly concedes that 100 degrees Celsius relies on standard rounding, conveniently ignoring Source 8 (en.wikipedia.org), which clarifies that the actual thermodynamic boiling point at 1 atmosphere is 99.97 degrees Celsius. Furthermore, the Proponent misrepresents Source 2 (webbook.nist.gov) by falsely equating its precise measurement of 373.17 Kelvin to exactly 100 degrees Celsius, when it actually converts to 100.02 degrees, proving the claim is a mere approximation rather than an absolute scientific fact.
Argument against
Although widely cited as a convenient shorthand, the claim is scientifically false because the actual thermodynamic boiling point of water at 1 atmosphere is 99.97 degrees Celsius, not exactly 100 (Source 8). Furthermore, precise measurements report an average boiling temperature of 373.17 Kelvin (100.02 degrees Celsius), confirming that the 100-degree figure is merely an inaccurate approximation rather than a strict factual absolute (Source 2).
The Opponent's own citations undercut their case: Source 2's 373.17 K equates to 99.02°C by their own arithmetic, but the true figure of 100.02°C actually falls on the side favoring the claim, and either way the deviation is within the ±0.04 K measurement uncertainty NIST itself reports, meaning the data affirms rather than refutes 100°C. This is a fallacy of false precision—treating a rounding artifact of the historical Celsius/Kelvin definitional shift (Source 8) as if it overturns the near-universal convention used by nineteen independent, verified sources including ScienceDirect, AccessScience, and multiple academic and engineering references, all of which state 100°C as the normal boiling point without qualification.
Panel Review
3 specialized AI experts evaluated the evidence and arguments.
Reviewer 1 — The Logic Examiner
The claim states a widely-used scientific convention: at 1 atm, water's normal boiling point is 100°C, and this is directly and repeatedly supported by 19 sources (Sources 1,4,5,7,10-16,18,19, etc.), with the minor deviations cited by the Opponent (99.97°C from Source 8's thermodynamic definition, 373.17K≈100.02°C from Source 2) falling within measurement uncertainty (±0.04K) or reflecting a post-1954 redefinition nuance rather than disproving the claim; the Opponent's argument commits a fallacy of false precision by treating a small definitional/measurement variance as falsifying a standard scientific convention that is itself defined as 100°C by construction (the Celsius scale was historically calibrated to water's boiling point). The overwhelming direct evidence supports the claim as true under the standard scientific convention, so the inferential chain from evidence to claim is sound despite the Opponent's attempt to exploit sub-tenth-degree precision differences.
Reviewer 2 — The Source Auditor
Highly reliable scientific and academic sources, including ScienceDirect (Source 1) and McGraw Hill's AccessScience (Source 4), confirm that the normal boiling point of water at 1 atmosphere of pressure is 100 degrees Celsius. While Wikipedia (Source 8) notes a slight thermodynamic deviation to 99.97 degrees Celsius due to modern temperature scale definitions, the overwhelming consensus of authoritative sources establishes 100 degrees Celsius as the universally accepted standard.
Reviewer 3 — The Precision Analyst
Multiple high-quality sources (1, 4, 5, 7, 10, 11, 12, 14–16, 18) directly state that water's normal boiling point is 100°C at 1 atm, matching the claim's quantities and scope exactly; NIST (2) and Wikipedia (8) note only sub-0.1°C definitional/measurement offsets that do not alter the conventional value. As worded, the claim is therefore true at the strength licensed by the evidence and standard scientific usage.
Panel summary
Authoritative scientific and academic references consistently identify 100°C as water's normal boiling point at 1 atmosphere. The inference is direct: boiling occurs when water's vapor pressure equals the surrounding pressure, and standard reference data support the stated pressure-temperature relationship. Quantitative analysis notes modern thermodynamic values near 99.97–100.02°C, depending on temperature-scale definitions and measurement conventions, but this negligible variation rounds to 100°C and does not materially alter the claim.