Boiling Point Temperature Element

Overview

Engineering reference data for Boiling Point Temperature Element in thermodynamics.

Key Formulas

Clausius-Clapeyron Equation

$\frac{d\ln P}{dT} = \frac{\Delta H_{vap}}{RT^2}$

Relates vapor pressure to temperature; defines the boiling curve.

Antoine Equation

$\log_{10} P = A - \frac{B}{C + T}$

Empirical correlation for vapor pressure vs. temperature. $A$, $B$, $C$ are substance-specific constants.

Boiling Point Elevation

$\Delta T_b = i \cdot K_b \cdot m$

Dissolving a solute raises the boiling point of the solvent.

Variables

Symbol	Description	Unit
$P$	Vapor pressure	Pa (or mmHg)
$T$	Absolute temperature	K (or °C for Antoine)
$\Delta H_{vap}$	Molar enthalpy of vaporization	J/mol
$R$	Universal gas constant	8.314 J/(mol·K)
$i$	Van't Hoff factor	—
$K_b$	Ebullioscopic constant	K·kg/mol
$m$	Molality of solute	mol/kg

Additional Engineering Notes

Air - Properties at Gas-Liquid Equilibrium Conditions

Ammonia - Thermophysical Properties

Benzene - Thermophysical properties

Calcium Chloride Water Solutions

Elements of the Periodic System

Ethanol - Thermophysical properties

Ethylene - Thermophysical Properties

Fuels - Boiling Points

Glycerine - Boiling and Freezing Points

Hydrocarbons - Physical Data

Liquids and Gases - Boiling Points

Metals - Boiling Temperatures

Nitrogen - Thermophysical Properties

Pentane - Thermophysical Properties

Refrigerants - Physical Properties

Toluene - Thermophysical Properties

Water - Boiling Points vs. Altitude

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See Also

• Air - Properties at Gas-Liquid Equilibrium Conditions
• Alcohols and Carboxylic Acids - Physical Data
• Ammonia - Thermophysical Properties
• Ammonia - Vapour Pressure at Gas-Liquid Equilibrium
• Benzene - Thermophysical properties
• Calcium Chloride Water Solutions
• Carbon Dioxide (CO₂) Properties & Characteristics: Density, Thermal Data & More
• Elements of the Periodic System
• Ethanol - Thermophysical properties
• Ethylene - Thermophysical Properties
• Ethylene Glycol Heat-Transfer Fluid Properties: Density, Data & Charts
• Fuels - Boiling Points
• Fusion and Evaporation Heat of common Materials
• Glycerine - Boiling and Freezing Points
• Hydrocarbon Mixtures - Average Boiling Points vs. Gravity and Molecular Weights
• Hydrocarbons - Physical Data
• Hydrocarbons, Alcohols and Acids - Boiling points
• Inorganic Compounds in Water - Melting and Boiling Temperature, Density and Solubility
• Liquids and Gases - Boiling Points
• Metals - Boiling Temperatures
• Nitrogen - Thermophysical Properties
• Organic Nitrogen Compounds - Physical Data
• Organic Sulfur Compounds - Physical Data
• Pentane - Thermophysical Properties
• Petroleum Products - Average Boiling Points
• Propylene Glycol based Heat-Transfer Fluids
• Refrigerants - Physical Properties
• Toluene - Thermophysical Properties
• Water - Boiling Points at Vacuum Pressure
• Water - Boiling Points vs. Altitude
• Water Boiling Point at Higher Pressures – Data & Calculator
• Water Properties: Vaporization Heat vs. Temperature - Charts and Calculator
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References

• Original Source

Factors Affecting Boiling Point

The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure surrounding the liquid. This transition temperature is not a fixed physical property but is influenced by several key factors:

• Pressure: The most significant factor. Boiling point increases with increasing external pressure and decreases with decreasing pressure. At standard atmospheric pressure (1 atm or 101.325 kPa), water boils at 100°C (212°F). On a high mountain where pressure is lower, water boils at a lower temperature. This relationship is quantitatively described by the Clausius-Clapeyron equation: $\frac{dP}{dT} = \frac{\Delta H_{vap}}{T \cdot \Delta V}$ where $\Delta H_{vap}$ is the molar enthalpy of vaporization, $T$ is the absolute temperature, and $\Delta V$ is the change in molar volume between the liquid and gas phases.

• Intermolecular Forces: Stronger forces between molecules (e.g., hydrogen bonding in water, polar interactions) require more energy (higher temperature) to overcome, leading to a higher boiling point. This explains the trend across similar compounds: for example, methane (CH₄) boils at -161.5°C, while propane (C₃H₈) boils at -42.1°C due to increased London dispersion forces with molecular size.

• Molecular Weight: For similar compounds (alkanes, noble gases), boiling point generally increases with molecular weight due to stronger London dispersion forces.

• Purity: The presence of dissolved substances (solutes) raises the boiling point of the solvent, a colligative property known as boiling point elevation ($\Delta T_b = i \cdot K_b \cdot m$), where $i$ is the van't Hoff factor, $K_b$ the ebullioscopic constant, and $m$ the molality.

Practical Considerations in Engineering

• Vacuum Systems: Many industrial processes, such as distillation, evaporative concentration, and some material drying operations, are performed under vacuum to lower the boiling point. This allows heat-sensitive materials to be processed at lower temperatures, reducing thermal degradation and saving energy.
• High-Pressure Applications: Systems like boilers, steam turbines, and geothermal power plants operate at elevated pressures to raise the boiling point of water, enabling the creation of high-temperature steam for efficient energy conversion.
• Altitude Corrections: Engineering calculations involving boiling points (e.g., designing equipment for mountainous regions) must account for the local atmospheric pressure. The boiling point of water decreases by approximately 1°F (0.56°C) for every 500 ft (150 m) increase in altitude.

Related Resources

This section provides a curated list of external documents and resources that expand on the boiling point data for various substances and conditions.

• Air - Properties at Gas-Liquid Equilibrium Conditions: Properties of air change along the boiling and condensation curves (temperature and pressure between triple point and critical point conditions). An air phase diagram is included.
• Alcohols and Carboxylic Acids - Physical Data: Molweight, melting and boiling point, density, pKa-values, as well as number of carbon and hydrogen atoms in molecules are given for 150 different alcohols and acids.
• Ammonia - Thermophysical Properties: Chemical, Physical and Thermal Properties of Ammonia. Phase diagram included.
• Ammonia - Vapour Pressure at Gas-Liquid Equilibrium: Figures and table with ammonia saturation pressure at boiling points, SI and Imperial units.
• Benzene - Thermophysical properties: Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included.
• Calcium Chloride Water Solutions: Freezing point, density, specific heat and dynamic viscosity of Calcium Chloride Water coolants.
• Carbon Dioxide (CO₂) Properties & Characteristics: Chemical, physical and thermal properties of carbon dioxide. Phase diagram included.
• Elements of the Periodic System: The elements of the periodic system with names, symbols, atomic numbers and weights, melting and boiling points, density, electronegativity and electron affinity, and electron configuration.
• Ethanol - Thermophysical properties: Chemical, physical and thermal properties of ethanol (also called alcohol or ethyl alcohol). Phase diagram included.
• Ethylene - Thermophysical Properties: Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.
• Ethylene Glycol Heat-Transfer Fluid Properties: Properties like freezing point, viscosity, specific gravity and specific heat of ethylene glycol based heat-transfer fluids, or brines.
• Fuels - Boiling Points: Fuels and their boiling points.
• Fusion and Evaporation Heat of common Materials: Melting points, heat of fusions, boiling points and heat to evaporate common substances - like hydrogen, water, gold and more.
• Glycerine - Boiling and Freezing Points: Boiling and freezing points of glycerine aqueous solutions.
• Hydrocarbon Mixtures - Average Boiling Points vs. Gravity and Molecular Weights: Formulas and examples of calculation of boiling point of hydrocarbon mixtures from gravity and molecular weight.
• Hydrocarbons - Physical Data: Molweight, melting and boiling point, density, flash point and autoignition temperature, as well as number of carbon and hydrogen atoms in each molecule for 200 different hydrocarbons.
• Hydrocarbons, Alcohols and Acids - Boiling points: Boiling temperatures (°C and °F) with varying carbon numbers up to C33.
• Inorganic Compounds in Water - Melting and Boiling Temperature, Density and Solubility: Physical constants for more than 280 common inorganic compounds. Density is given for the actual state at 25°C and for liquid phase at melting point temperature.
• Liquids and Gases - Boiling Points: Boiling temperatures for common liquids and gases - acetone, butane, propane and more.
• Melting and Boiling Temperatures - Evaporation and Melting Heats common Materials: Melting and boiling point temperatures, latent heat of evaporation, and melting heat of common substances like copper, gold, lead and more - SI units.
• Metals - Boiling Temperatures: Metals and their boiling temperatures.
• Nitrogen - Thermophysical Properties: Chemical, Physical and Thermal Properties of Nitrogen - N2.
• Organic Nitrogen Compounds - Physical Data: Boiling and melting points of amines, diamines, pyrroles, pyridines, piperidines and quinolines shown together with their molecular structures, as well as molweights and density.
• Organic Sulfur Compounds - Physical Data: Boiling and melting points of thoils, sulfides, disulfides and thiophenes shown together with molecular structures, as well as molweights and density.
• Pentane - Thermophysical Properties: Chemical, physical and thermal properties of pentane, also called n-pentane. Phase diagram included.
• Petroleum Products - Average Boiling Points: Definition, explanation and examples of calculation of various types of average boiling point of petroleum products and other mixtures of hydrocarbons: VABP, MABP, WABP, CABP and MeABP.
• Propylene Glycol based Heat-Transfer Fluids: Freezing points of propylene glycol based heat-transfer fluids suitable for the food processing industry.
• Refrigerants - Physical Properties: Physical properties of refrigerants - molecular weight, boiling, freezing and critical points.
• Toluene - Thermophysical Properties: Chemical, physical and thermal properties of toluene, also called methylbenzene, toluol and phenylmethane. Phase diagram included.
• Water - Boiling Points at Vacuum Pressure: Online calculator, figures and tables.

Boiling Point Calculation Formulas

The following formulas are essential for engineering calculations involving boiling point temperatures under varying conditions.

Clausius-Clapeyron Equation

Relates the vapor pressure of a liquid to its temperature: $\frac{d\ln P}{dT} = \frac{\Delta H_{vap}}{RT^2}$ Where $P$ is vapor pressure, $T$ is temperature, $\Delta H_{vap}$ is the enthalpy of vaporization, and $R$ is the universal gas constant.

Antoine Equation

An empirical formula for relating vapor pressure to temperature: $\log_{10} P = A - \frac{B}{C + T}$ Where $P$ is vapor pressure (typically in mmHg), $T$ is temperature (°C), and $A, B, C$ are substance-specific constants.

Key Compounds and Reference Data

The following are key compound categories with references to their boiling point and thermophysical data, as found in standard engineering resources.

• Air: Properties along the gas-liquid equilibrium curve, including a phase diagram.
• Ammonia (NH₃): Vapour pressure at boiling points, thermophysical properties, and phase diagram.
• Benzene (C₆H₆): Thermophysical properties and phase diagram.
• Carbon Dioxide (CO₂): Properties including density and thermal data with phase diagram.
• Ethanol (C₂H₅OH): Thermophysical properties and phase diagram.
• Ethylene (C₂H₄): Thermophysical properties and phase diagram.
• Ethylene Glycol: Properties of heat-transfer fluids (density, viscosity, specific heat).
• Glycerine: Boiling and freezing points for aqueous solutions.
• Hydrocarbon Mixtures: Formulas for calculating average boiling points from gravity and molecular weight.
• Petroleum Products: Definitions and calculations for average boiling points (VABP, MABP, WABP, CABP, MeABP).
• Refrigerants: Physical properties including molecular weight and critical points.
• Water: Boiling points at vacuum pressures.

This structured reference helps in locating detailed data for specific engineering applications.

Substance Categories and Applications

Average Boiling Point Types for Petroleum

Petroleum products are complex mixtures requiring different averaging methods to characterize their boiling behavior:

Abbreviation	Full Name	Calculation Basis	Primary Use
WABP	Weight Average Boiling Point	Weight fraction	General characterization
MABP	Molar Average Boiling Point	Mole fraction	Thermodynamic calculations
VABP	Volume Average Boiling Point	Volume fraction	ASTM distillation data
CABP	Characteristic Average Boiling Point	Mid-boiling point	Correlation methods
MeABP	Mean Average Boiling Point	Mean of MABP and VABP	Property estimation

These averages are related through the following general relationship:

$\text{MeABP} \approx \frac{\text{MABP} + \text{VABP}}{2}$

For hydrocarbon mixtures, the average boiling point can be estimated from specific gravity ($SG$) and molecular weight ($MW$) using empirical correlations specific to the petroleum fraction.

Boiling Point at Reduced Pressure

Many engineering applications require boiling point data at pressures other than standard atmospheric (101.325 kPa). The relationship between boiling point and pressure for vacuum systems follows the Antoine equation:

$\log_{10} P = A - \frac{B}{T + C}$

where $P$ is vapor pressure (mmHg), $T$ is temperature (°C), and $A$, $B$, $C$ are substance-specific constants. Water boiling points at various vacuum pressures are commonly referenced in distillation and drying applications.