The key difference between normal boiling point and standard boiling point is that the boiling temperature at 1 atm is the normal boiling point, whereas the boiling temperature at 1 bar is the standard boiling point.
The boiling point of a substance is the temperature at which the vapour pressure of a liquid becomes equal to the pressure surrounding the liquid. Thus, at this temperature, the state of the substance changes from liquid to vapour. However, the boiling point varies depending on some factors such as the strength of the intermolecular forces between the molecules of the liquid, branching of the molecule, the number of carbon atoms in hydrocarbons, etc. Furthermore, there are two types of boiling points as normal and standard boiling point. These two are different from each other depending on the atmospheric pressure at which we measure the boiling point.
CONTENTS
1. Overview and Key Difference
2. What is Normal Boiling Point
3. What is Standard Boiling Point
4. Side by Side Comparison – Normal Boiling Point vs Standard Boiling Point in Tabular Form
5. Summary
What is Normal Boiling Point?
Normal boiling point is the boiling temperature of a liquid at 1 atm pressure. Moreover, atmospheric boiling point and atmospheric pressure boiling point are two synonyms for this term.
Figure 01: Boiling Water
At this boiling temperature, the vapour pressure of the liquid equals 1 atm (which is the defined atmospheric pressure at sea level. At this point, the vapour pressure of the liquid overcomes the atmospheric pressure and as a result, bubbles of liquid vapour forms.
What is Standard Boiling Point?
Standard boiling point is the boiling temperature of a liquid at 1 bar. Also, it is this temperature we consider as the IUPAC defined boiling point (since 1982). For example, the standard boiling point of water is 99.61 °C at 1 bar.
What is the Difference Between Normal Boiling Point and Standard Boiling Point?
Normal and standard boiling points are different from each other according to the pressure at which we measure the boiling point. Hence, the key difference between normal boiling point and standard boiling point is that the boiling temperature at 1 atm is the normal boiling point, whereas the boiling temperature at 1 bar is the standard boiling point. For example, the normal boiling point of water is 99.97 °C at 1 atm while the standard boiling point of water at 1 bar is 99.61 °C.
Summary – Normal Boiling Point vs Standard Boiling Point
According to the pressure at which we measure the boiling point of a liquid, the boiling temperatures of the same liquid may differ. The key difference between normal boiling point and standard boiling point is that the boiling temperature at 1 atm is the normal boiling point, whereas the boiling temperature at 1 bar is the standard boiling point.
Reference:
1. Helmenstine, Anne Marie, “Normal Boiling Point Definition (Chemistry).” ThoughtCo, Feb. 21, 2019, Available here.
Image Courtesy:
1. “Boiling Water” By Scott Akerman (CC BY 2.0) via Flickr