The key difference between boiling point and melting point is that boiling point is the temperature at which a liquid state changes to its gaseous state whereas melting point is the temperature at which a solid state changes into a liquid state.
There are three states of matter: solid state, liquid state and gaseous state. Substances can change from one particular state to another if we vary the temperature of that substance. Upon heating, usually a solid change into its liquid state; and upon further heating, it changes into its gaseous state. In contrast, if we cool a gaseous compound, it changes into the liquid state, followed by a solid state upon further cooling. However, there are some solid substances that can directly go to the gaseous state without going through the liquid state (we call this sublimation), and vice versa.
CONTENTS
1. Overview and Key Difference
2. What is Boiling Point
3. What is Melting Point
4. Side by Side Comparison – Boiling Point vs Melting Point in Tabular Form
6. Summary
What is Boiling Point?
Boiling point is a property of a liquid. The boiling point is the temperature at which the vapour pressure of the liquid is equal to the external pressure on the liquid. Pressure is a major factor that affects the boiling point; higher the external pressure on a substance, higher the boiling point. Thus, this is the simple theory behind pressure cookers. A pressure cooker is a cooker that traps the vapour from the heated water inside it. The high amount of vapour inside the container makes external pressure on the liquid higher. Consequently, this high pressure results in a higher boiling point. Also, this theory is very useful, especially in higher altitudes. Usually, water boils at 1000C. Since the atmospheric pressure is lower at higher altitudes, water will boil between 80 0C – 90 0C. And, this will cause undercooked meals.
Figure 01: Water Boiling at Boiling Point
A liquid boils when it exceeds its saturation temperature at the corresponding saturation pressure. The saturation temperature is the temperature corresponding to the highest thermal energy the liquid can hold without changing its state to vapour at the given pressure. The saturation temperature is also equivalent to the boiling point of the liquid. Boiling occurs when the thermal energy of the liquid is enough to break the intermolecular bonds. The normal boiling point is the saturation temperature at atmospheric pressure. Moreover, the boiling point varies only between the triple point and critical point of the liquid.
What is Melting Point?
Melting point is a property of a solid. The melting point is the temperature at which the solid turns into a liquid. More precisely, the melting point is the temperature when the liquid state and the solid state remain in thermal equilibrium with each other.
Figure 2: Melting Ice
The melting point and the freezing point of a substance might not be the same. For example, agar melts at 85 0C, but it solidifies back at 31 0C to 40 0C. Intermolecular bonds and molecular weight mostly define the melting point. Some solids like glass don’t have a specific melting point. They simply undergo a smooth transition from solid to liquid.
What is the Difference Between Boiling Point and Melting Point?
Boiling point and melting point are properties of substances. The key difference between boiling point and melting point is that boiling point is the temperature at which a liquid state changes to its gaseous state whereas melting point is the temperature at which a solid state changes into a liquid state. Therefore, the boiling point is defined for a liquid state while the melting point is defined for a solid state.
The below info-graphic presents more details on the difference between boiling point and melting point.
Summary – Boiling Point vs Melting Point
Both boiling point and melting point are properties of matter. They play a very important role when it comes to describing a material. The key difference between boiling point and melting point is that boiling point is the temperature at which a liquid state changes to its gaseous state whereas melting point is the temperature at which a solid state changes into a liquid state.
Reference:
1. “Boiling Point.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 20 Feb. 2018, Available here.
2.“Melting Point.” Wikipedia, Wikimedia Foundation, 12 May 2019, Available here.
Image Courtesy:
1. “Boiling Water” By Scott Akerman (CC BY 2.0) via Flickr
2. “Melting ice thermometer” By Ulflund – Own work (CC0) via Commons Wikimedia