how can the boiling point be negative?

Boiling point refers to the temperature at which a substance undergoes a phase transition from liquid to gas. This value is usually significant in chemistry since it enables researchers to determine the chemical properties of a substance. Most substances display positive boiling points; however, some can possess negative boiling points, which means that they boil at temperatures lower than their melting point.

In this article, we shall discuss how substances can have negative boiling points and explore the implications and controversies surrounding this phenomenon.


Definition of boiling point

The boiling point is the temperature at which a substance changes from its liquid state into its gas state. All substances that boil exist at their boiling point temperature as both a liquid and gas.

Importance of understanding boiling points in chemistry

Determination of boiling points plays an essential role in various areas of chemistry such as process engineering, material science, and analytical chemistry. It helps in identifying pure compounds or creating mixtures of different substances by distillation or fractional distillation methods.

Brief background on negative boiling points

Although it may seem counterintuitive or impossible for a substance to have a negative-boiling-point value, there are several documented examples where this phenomenon occurs.

Factors Affecting Boiling Points

Relationship between intermolecular forces and boiling points

Boiling points vary among different molecules primarily because of differences in intermolecular forces. Stronger intermolecular forces require more energy (heat) to overcome interactions between molecules during evaporation and thus lead to higher boiling temperatures.

The effects of pressure and altitude on boiling points

Pressure affects the rate at which vapor pressure accelerates leading to increased evaporation rate. At higher altitudes where atmospheric pressure is low, less heat energy is required for evaporation; as a result, liquids boil faster than usual with temperatures lower than usual.

Comparison between normal, high, and low boiling point substances

Different categories of substances display varying boiling points. Volatile liquids have low boiling points, while non-volatile substances generally have higher boiling points.

Understanding Negative Boiling Points

Explanation of negative boiling points

Negative boiling point is an unusual and relatively rare phenomenon that occurs when the pressure is insufficient to maintain a liquid’s stable state. Under these conditions, once the temperature surpasses the substance’s melting point, the material undergoes sublimation without transitioning through a liquid phase and stops potentially hundreds of degrees below its melting temperature as it forms gas.

Examples of substances with negative boiling points

One classic example of a compound with a negative-boiling-point value is Carbon dioxide (CO2). This molecule exists as dry ice at ambient pressures and sublimes into gaseous carbon dioxide when heated above -78°C (-109°F). Likewise, nitrogen (N2) exhibits a strongly negative-boiling-point trend due to weak intermolecular forces between its molecules.

Factors that contribute to substances having negative boiling points

The primary contributors to this phenomenon are weak intermolecular forces within molecules and reduced pressure. If the compound remains chemically stable without decomposing or reacting under lower atmospheric pressures instead of vaporizing into gas, it can exist in its solid state till elevated temperatures are applied. As heat continues to increase, the solid evaporates directly into vapour gas upon reaching satisfactory enthalpy threshold leading to sublimation.

Thermodynamics behind Negative Boiling Points

Explanation of thermodynamics principles: enthalpy, entropy, and gibbs free energy

Thermodynamics refers to natural sciences that studies relationships amongst various effects like heat transfer concerned with thermal behaviour phenomena involved in nature systems. The core concepts involve Enthalpy i.e total amount of thermal energy exchange between different subsystems for attaining equilibrium;_entropy refers to distribution factor represented by random motion displacement measure;and Gibbs Free Energy index can predict the way substances interacts with each other at equilibrium.

Relationship between thermodynamics principles and negative boiling points

Materials with negative boiling points have distinct, atypical characteristics that are not taken into account in conventional thermodynamic predictions. Such materials display a unique phase transition signature that indicates that they undergo a transformation from a solid to vapour without transitioning through the liquid phase. This occurs when certain materials are subjected to conditions of limited pressure at equilibria where the enthalpy magnitude driving the process is higher than the free energy cost of reaching sublimation point.

Observing Negative Boiling Points

Methods for observing negative boiling points in the lab

Researchers can utilize several techniques such as Differential scanning calorimetry (DSC), Laser heating method, and suppression of surface tension method dependent on experiment requirements or substance being investigated for obtaining accurate estimate information concerning negative boiling points in lab test setup.

Experimental procedures for measuring negative boiling points

Various experimental methods involve application of astute control over parameters around samples in order to determine changes during annealing/deposition phases. Researchers may use dynamic conductivity studies or measurement of film growth rate changes due to controlled heating/ cooling adjusted against time intervals under low vacuum systems whose parameters are set up accurately prior to starting test trials.

Practical Applications of Negative Boiling Points

Industrial uses of substances with negative boiling points

Although rarely discussed topics, many industrial processes benefit from having heat regulation potential which utilizes compounds displaying weak intermolecular forces like nitrogen & CO2 for exact reduction purposes per industrial sector demands.

Benefits and drawbacks of using substances with negative boiling points

The advantages of utilizing compounds exhibiting weak intermolecular force nature lies mainly within their ability to provide precise temperature control over specific reaction conditions without disturbing surrounding environment whereas disadvantage could be lack in safety data about such compounds risking inputting end-users safety at risk if mis-handled or used while recognizing only theoretical results alone without proper test trials results.

Controversies and Unresolved Issues

Conflicting studies on the existence of a true negative-boiling point

One controversy regarding a true negative-boiling-point is within the community and suggests the phenomenon is not realistic or doesn’t actually occur in any meaningful sense. Other scientists argue that there is not enough consensus about what constitutes a true negative boiling point, and that more research should be conducted to resolve this issue.

Ethical concerns around industrial use of compounds with low to no safety data.

Another issue raised by critics is the lack of adequate information on the safety considerations associated with using substances displaying weak intermolecular forces. Implementing these compounds into industrial applications, either knowingly or unknowingly, may lead to risky or catastrophic events concerning environmental & human health if proper precautionary measures are not taken priorly after weighing up potential advantages against projected risk factors during manufacturing processes as mandated by regulatory bodies.


In conclusion, a negative-boiling-point scenario for substances isn’t an impossible concept; it’s when certain materials undergo sublimation without transitioning through the liquid phase under equilibrium conditions where pressure isn’t maintained resulting in surprising below-freezing boiling temperatures. Substances exhibiting negative boilings points can provide valuable benefits for various industrial applications but due majorly because of insufficient safety data surrounding such compounds combined with conflicting views about their existence mandate increased research efforts must be undertaken, followed by risk mitigation strategies before implementing them commercially.


  1. Q: Can water really boil at a negative temperature? A: Yes, it can. Liquids can boil at temperatures lower than their normal boiling point when they are subjected to reduced pressure or a change in the composition of the pressure around them.
  2. Q: Why does lowering the pressure cause the boiling point to drop below zero? A: Lowering the air pressure reduces the atmospheric pressure that surrounds a liquid and makes it easier for its molecules to escape into the gas phase by reducing the amount of energy needed to overcome intermolecular forces. As a result, less heat is required to vaporize the liquid, causing its boiling point to decrease.
  3. Q: Are there any practical applications of liquids boiling at negative temperatures? A: Yes, there are many examples of how this phenomenon is used in various scientific and industrial processes, such as vacuum distillation, freeze-drying food, and manufacturing semiconductors.
  4. Q: Is a negative boiling point always an indication that something is wrong with the liquid? A: Not necessarily. In some cases, substances like helium and nitrogen have negative boiling points under normal conditions due to their particular molecular properties and intermolecular interactions. However, some other liquids may have negative boiling points when they are contaminated or degraded by chemical reactions or changes in their physical environment.