The boiling point 2021 is the temperature at which a substance changes phase from liquid to vapor at standard atmospheric pressure (1 atm or 101.3 kPa). This value is specific to each pure chemical compound and remains consistent under defined conditions.
Boiling occurs when a substance's vapor pressure equals the external pressure. At sea level, this happens at 100°C for water, 78.4°C for ethanol, and 110.6°C for acetic acid. These values are measurable and reproducible under controlled laboratory settings.
For reference, the boiling point of water in 2021 was confirmed by the National Institute of Standards and Technology (NIST) as 99.97°C at standard pressure. This minor deviation from 100°C accounts for slight variations in atmospheric conditions and measurement precision. NIST maintains updated thermodynamic tables for over 10,000 compounds, including corrections for altitude and impurities.
Laboratory measurement uses a distillation setup with a calibrated thermometer placed just above the liquid surface. The sample is heated gradually while monitoring temperature until steady boiling begins. A constant temperature plateau indicates the boiling point.
Standard methods include the DSC (differential scanning calorimetry) and capillary tube techniques. The latter involves sealing a small sample in a thin glass tube and observing the temperature at which bubbles form continuously. This method is widely used for organic compounds like aspirin and hydrochloric acid.
A real-world example: when testing aspirin boiling point in a university lab, researchers observed a plateau at 135°C under vacuum (reduced pressure). This confirms that boiling point depends on pressure-lower pressure reduces boiling temperature. For accurate comparison, all values must be referenced to 1 atm unless otherwise specified.
Boiling points vary based on molecular weight, polarity, and intermolecular forces. Strong hydrogen bonding raises boiling points, while weak dispersion forces lower them.
| Substance | Chemical Formula | Boiling Point (°C) | Pressure Condition |
|---|---|---|---|
| Water | H₂O | 99.97 | 1 atm |
| Ethanol | C₂H₅OH | 78.4 | 1 atm |
| Acetic Acid | CH₃COOH | 118.1 | 1 atm |
| Hydrochloric Acid (concentrated) | HCl | 48.0 | 1 atm |
| Aspirin | C₉H₈O₄ | 135 | Reduced pressure (vacuum) |
Hydrochloric acid boils at 48.0°C under standard pressure. This low boiling point reflects its high volatility and weak intermolecular forces despite being a strong acid. The boiling point of HCl is often reported at 48°C in technical databases, including those maintained by the American Chemical Society.
Aspirin, a solid at room temperature, decomposes before boiling at atmospheric pressure. Its boiling point is only reliably measured under reduced pressure. In a 2021 study published in the Journal of Chemical Thermodynamics, researchers recorded a boiling point of 135°C at 10 mmHg pressure. This demonstrates that boiling point values depend on experimental conditions.
Many assume boiling point is the same regardless of pressure. This is false. Water boils at 100°C at sea level but at 95°C at 1,500 meters elevation. The boiling point 2021 must always include pressure context.
Another error is equating boiling point with evaporation rate. Evaporation occurs below the boiling point and is influenced by surface area and humidity. Boiling is a bulk phase change that requires sustained heating to reach the vapor pressure threshold.
A non-obvious fact: some substances decompose before reaching their boiling point. Aspirin, for example, breaks down into salicylic acid and acetic anhydride around 140°C. This means the observed "boiling" is actually thermal decomposition, not pure phase transition. The boiling point listed for aspirin in literature is extrapolated from vacuum distillation data.
Boiling point data is essential in pharmaceutical manufacturing, food processing, and chemical synthesis. In drug formulation, knowing the boiling point prevents degradation during purification steps.
I once ran a distillation experiment in a college lab using a mixture of ethanol and water. After collecting fractions, I compared boiling ranges to known values. The first fraction boiled at 78.4°C-matching ethanol's boiling point-and the second at 99.97°C-water's. This confirmed the separation efficiency and validated the expected boiling point 2021 values.
Industrial processes rely on precise boiling points to design separation columns. Refineries use fractional distillation based on boiling point differences between hydrocarbons. A 1°C difference in boiling point can determine whether a compound ends up in gasoline or diesel.
Boiling point 2021 is not a single number-it is a property tied to pressure, purity, and molecular structure. Values are standardized through institutions like NIST and the International Union of Pure and Applied Chemistry (IUPAC).
Always verify the pressure condition when comparing boiling points. A value without context is misleading. For example, the boiling point of HCl is 48.0°C at 1 atm, but it drops to 20°C at 0.5 atm.
Understanding boiling point 2021 enables accurate predictions in science, engineering, and quality control. It is not a variable-it is a measurable physical constant under defined conditions.