Dhristi JEE 2022-24

Introduction to Boiling Point

A liquid's boiling point is the temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure of the liquid. The liquid is transformed into a vapour at this temperature. It is at this point, with the addition of heat that the liquid transforms into vapour without any increase in the temperature. 


Elaborate Description of Boiling Point

As a liquid is heated, its vapour pressure increases until it is equal to the pressure of the gas surrounding it. Bubbles of vaporized liquid (gas) are then formed within the liquid, rising to the surface where they eventually burst before being released into the air. It is important to note that, at the boiling temperature, the vapour inside the bubble exerts enough pressure to keep the bubble from collapsing. The molecules of a liquid must be able to overcome the forces of attraction between them to create vapour.


The liquid's boiling point depends on the surrounding pressure. It has a higher boiling point than the boiling point at normal atmospheric pressure while the fluid is at high pressure. For a given pressure, the boiling point of various liquids is different. The standard boiling point of a liquid was described in 1982 by IUPAC as the temperature at which the liquid boils under a pressure of 1 bar. For example, the boiling point of liquid a is x under normal atmospheric conditions of 1 bar but when liquid a is taken to an elevation of 10,000 ft. the boiling point of that liquid will become considerably lower than x. 


For any substance, the boiling point is the temperature point at which the material in the liquid stage converts into the gas phase. This occurs with water at 100 degrees centigrade. Based on the ice/water melting point and the liquid water/vapour boiling point, the Celsius scale was developed. Each material bears a boiling point of its own. The temperature starts to rise again as all the particles in the liquid phase have been converted into the gas phase, as long as heat is still being added to the surrounding system. As the temperature begins to rise, so does the kinetic energy of the particle.


Factors Affecting the Boiling Point

  1. Pressure

  • When it is less than 1 bar, the boiling point of a liquid is lower than its normal boiling point. 

  • When it is equal to 1 bar, the boiling point of a liquid is at its normal boiling point. 

  • When it is more than 1 bar, the boiling point of a liquid is greater than its normal boiling point. 

  1. Types of Molecules

The types of molecules that a liquid is composed of determine its boiling point. If the molecules' intermolecular forces are equal to - 

  • Relatively strong, the boiling point of a liquid will be relatively high.

  • Relatively weak, the boiling point of a liquid will be relatively low. 


Boiling Point of Water

In two ways, water may boil, increase the temperature or decrease the air pressure. It is the air pressure at sea level that causes water to boil at 100℃. In a vacuum, where there is no air, water can boil at a much lower temperature. That is, body temperature would be sufficient to allow the blood to boil with water, if not for the skin that holds the blood pressurized. So, speaking of the boiling point of water, it boils at low air pressure at temperatures significantly below 100℃. 


In general, the melting point is defined as the point at which materials move from a solid to a liquid. The melting point of that liquid is called the temperature at which the solid changes its state to liquid at atmospheric pressure. This is the point of equilibrium at which both the liquid and solid phases occur. The substance's melting point often varies with pressure and is defined at the normal pressure.


Boiling Point of Ethanol

Ethanol has a boiling point of 78°C (173 °F), with a molecular weight (MW) of 46.


Methanol Boiling Point

Methanol has a Boiling point of 64.7°C (148.5 °F; 337.8 K)


Boiling Point of Milk

The cow's milk's boiling point is about 203 ° F (95 ° C)


Boiling Point of Alcohol

The boiling points of alcohols of equal molecular weights are much higher than those of alkanes. Ethanol, for example, has a boiling point of 78 °C (173 °F) with a molecular weight (MW) of 46, while propane (MW 44) has a boiling point of −42 °C (−44 °F).


Melting Point

In general, the melting point is defined as the point at which materials move from a solid to a liquid. 


The melting point of that liquid is called the temperature at which the solid changes its state to liquid at atmospheric pressure. This is the point of equilibrium at which both the liquid and solid phases occur. The substance's melting point often varies with pressure and is defined at the normal pressure. 


The turbulent vibrations of the atoms in a solid substance overcome the forces of attraction operating within the solid at its melting point. Similar to the boiling point, the melting point of a substance is dependent upon the attractive forces taking place inside the solid. Note, the melting point of a substance in a solid state is the same as the freezing point of the same substance in a liquid state. It is at that temperature that the solid and the liquid states of the substance are in equilibrium. 


Melting Point of Ice

32°F (0 °C) is the melting point of ice at which it, as a solid, transforms into water, a liquid.


Melting Point of Diamond

The ultimate diamond melting point is around 7,280° Fahrenheit (4,027° Celsius).


Did you Know?

Water is unique in that it is less dense than the liquid form of the solid form, ice, which is why ice floats. 


Water, since it dissolves more substances than any other liquid, is considered the "universal solvent" This implies that it brings along valuable chemicals, minerals, and nutrients everywhere water goes, either through the earth or through our bodies. 


The neutral pH of pure water is 7, which is neither acidic (less than 7) nor basic (greater than 7). It is very sticky, meaning water molecules bind to each other, the water molecule is extremely cohesive. Of the non-metallic liquids, water is the most coherent. The water molecule is highly adhesive.


Learn more about the concept of the natural phenomenon of a boiling point along with examples at Vedantu. Get excellent study material to understand this phenomenon and understand it well. Make your conceptual foundation stronger and answer questions easily. 

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FAQs (Frequently Asked Questions)

1. Is boiling point the same as melting?

Mixtures often appear to melt at temperatures below the pure solids' melting points. It gradually reaches a temperature when a liquid is heated at which the vapour pressure is high enough to form bubbles within the liquid's body. The boiling point is called this temperature.


Temperature is the speed at which the molecules of a substance move. The higher the temperature, the quicker the molecules vibrate. The melting point is the temperature at which the molecules of a solid vibrate strongly enough that they can move past each other and form a liquid. The boiling point, however, is the temperature at which the vapour from the liquid is pushing the surrounding air just as hard as it is pushing back. Given that, both boiling and melting points are dependent on pressure, therefore some substances have the same boiling and melting point. 

2. What is the boiling point of water?

A substance's boiling point is the temperature at which a liquid's vapour pressure equals the pressure surrounding the liquid, and the liquid transforms into a vapour. A liquid's boiling point varies depending on the ambient pressure surrounding it. Water at sea level, under normal atmospheric pressure, boils at 100°C. It can boil at radically different temperatures depending upon the altitude, surrounding air, and vapour pressure. For more information about this, check out the free study materials which can be downloaded from the Vedantu app and website Vedantu.

3. Why is the boiling point so important?

Significant knowledge about their physical properties and structural characteristics can be given by the boiling point of organic compounds. The boiling point helps define a compound and describe it. A liquid has a higher boiling point at a higher pressure than when the liquid is at lower atmospheric pressure. It indicates the physical state of a substance at normal temperatures and atmospheric pressure. The boiling point of a chemical is also very important for safe transportation and storage. 

4. What is the boiling point?

The boiling point is the temperature at which a liquid is converted into vapour. The boiling point is referred to as the temperature at which the pressure exerted by the air surrounding a liquid is equal to the pressure exerted by the vapour of the liquid. Once a liquid begins to boil, the temperature remains the same until all the remaining liquid has been converted into vapour. The boiling point of a liquid can vary depending on the surrounding environmental pressure. 

5. What is the melting point?

The melting point is the temperature at which the molecules of a solid particle vibrate quickly enough, resulting in the conversion of the solid to a liquid due to sufficient heat. It is the temperature at which both the solid and liquid forms of a substance exist in equilibrium because, for a particular substance, the solid state’s melting point is the liquid state’s freezing point, depending on factors like said substance’s purity and surrounding atmospheric pressure. 

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