Boiling point is a physical property because it is the temperature at which a substance changes from a liquid to a gas phase without undergoing any chemical reactions. It is solely dependent on the intermolecular forces within the material and does not involve any alteration in its chemical composition. 1 2
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Key Takeaways: Is Boiling Point a Physical or Chemical Property?
- Boiling point is a physical property because it is the temperature at which a substance changes from a liquid to a gas phase without any chemical reactions.
- Physical properties can be observed and measured without altering the substance’s chemical composition.
- Chemical properties, on the other hand, involve changes in the substance’s molecular or atomic structure and its interactions with other substances. Boiling point does not lead to such changes.
Why is boiling point a physical property?
Boiling point is considered a physical property because it is a characteristic of a substance that can be observed and measured without changing its chemical composition. 3 Physical properties are inherent characteristics of a material that can be determined through physical means, such as temperature, pressure, or density, and they help to identify and classify substances.
The boiling point specifically refers to the temperature at which a substance changes its state from a liquid to a gas at a given pressure. At the boiling point, the vapor pressure of the liquid becomes equal to the atmospheric pressure, causing bubbles to form throughout the liquid and eventually turning it into a gas. 4
There are several reasons why boiling point is classified as a physical property:
- It is independent of the amount of substance: The boiling point of a substance remains constant under normal atmospheric pressure regardless of the quantity of the material present. For example, water boils at 100 degrees Celsius at sea level, 5 whether you have a cup of water or a large pot.
- It is specific to the substance: Different substances have distinct boiling points that can be used to identify and differentiate them. For instance, water has a boiling point of 100 degrees Celsius, while ethanol has a boiling point of around 78 degrees Celsius. 6 7
- It is reproducible: Boiling points can be measured accurately and reproduced under specific conditions, making them valuable for scientific and practical purposes.
- It reflects the intermolecular forces: Boiling points are influenced by the strength of intermolecular forces within a substance. Substances with stronger intermolecular forces generally have higher boiling points. This property helps in understanding the nature of molecular interactions within the material.
- It is related to phase transitions: Boiling points are critical for studying phase transitions, as they mark the boundary between the liquid and gas phases of a substance.
Overall, the boiling point is an essential physical property used in various scientific, industrial, and everyday applications, such as in the design of distillation processes, cooking, and in the pharmaceutical and chemical industries.
Why is boiling point not a chemical property?
Boiling point is not considered a chemical property because it does not involve any changes in the chemical composition or identity of the substance. Chemical properties are characteristics that describe how a substance interacts with other substances, undergoes chemical reactions, or transforms into new substances with different properties. 8
Boiling point, on the other hand, is a physical property because it solely depends on the strength of intermolecular forces and the temperature and pressure conditions, without altering the substance’s fundamental chemical identity.
When a substance boils, it transitions from a liquid to a gas phase, but the chemical composition of the substance remains the same.
Chemical properties, on the contrary, involve changes at the molecular or atomic level. These properties include reactivity, flammability, acidity, and other characteristics that describe how a substance interacts with other substances to form new chemical bonds and undergo chemical transformations. 9
To summarize, boiling point is a physical property because it relates to the state of matter of a substance (liquid to gas phase transition) based on external conditions, whereas chemical properties involve changes in the internal structure and composition of the substance resulting from chemical reactions and interactions with other substances.
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- Boiling point – Wikipedia. (n.d.). Boiling Point – Wikipedia. https://en.wikipedia.org/wiki/Boiling_point
- Determination of Boiling Points by Capillary Method – Procedure | Lab: Chemistry | JoVE. (n.d.). Determination of Boiling Points by Capillary Method – Procedure | Lab: Chemistry | JoVE. https://www.jove.com/science-education/11193/boiling-points
- 3.5: Differences in Matter- Physical and Chemical Properties. (2016, April 4). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry/03%3A_Matter_and_Energy/3.05%3A_Differences_in_Matter-_Physical_and_Chemical_Properties
- Vapor Pressure & Boiling. (n.d.). Vapor Pressure & Boiling. https://terpconnect.umd.edu/~wbreslyn/chemistry/pressure/vapor-pressure.html
- At what temperature does water boil? Explaining water’s boiling point and how long it will take. (n.d.). USA TODAY. https://www.usatoday.com/story/life/food-dining/2022/07/19/at-what-temperature-does-water-boil/10088297002/
- Alcohol – Boiling Point, Solubility, Flammability. (n.d.). Encyclopedia Britannica. https://www.britannica.com/science/alcohol
- Uiuc.edu http://www.chem.uiuc.edu/organic/Alcohols/Chapter%206/sec6-2/6-2.htm
- 1.3: Properties of Matter. (2014, November 18). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/01%3A_Introduction_-_Matter_and_Measurement/1.03%3A_Properties_of_Matter
- Physical and Chemical Properties – Chemistry. Physical and Chemical Properties – Chemistry. https://pressbooks-dev.oer.hawaii.edu/chemistry/chapter/physical-and-chemical-properties/