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Melting and Boiling Point: Learn Their Definitions, Differences, Determinations and Affecting Factors.
IMPORTANT LINKS
States of Matter
Have you ever noticed how ice melts into water or how water turns into streams when heated?
These changes happen at specific temperatures called the melting point and boiling point. Understanding these points is important. They will help us know how a substance behaves when heated or cooled. In this article, we’ll explore what melting and boiling points are, how they are different, how we measure them, and what factors can change them. Whether you’re preparing for an exam or just curious, this guide will make it all easy to understand.
Melting and Boiling Point
Melting point: The temperature at which a substance transitions from a solid to a liquid state is known as its melting point. The solid and liquid phases are in equilibrium at the melting point. A solid's temperature rises when heat is added to it until it reaches the melting point. Pressure also affects melting point, typically reported at a standard pressure such as 1 atmosphere or 100 kPa.
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A liquid's boiling point changes depending on the pressure being applied, which is the average atmospheric pressure at sea level (760 mm [29.92 inches] of mercury). Water boils at sea level at 100° C (212° F). Therefore, lower boiling point temperatures are observed at greater altitudes.
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- Boiling point: The temperature at which a liquid's vapor pressure equals the pressure around it and the liquid transforms into a vapor is known as the boiling point of a substance. At this temperature, adding heat causes the liquid to turn into its vapor without raising the temperature.
- Freezing Point: The freezing point of a liquid is the temperature at which it turns into a solid. Similar to the melting point, the freezing point typically rises with increasing pressure. In the case of mixtures and for some organic substances, such as lipids, the freezing point is lower than the melting point.
Difference between Melting and Boiling Points
The key differences between the melting and boiling point are discussed in the table below:
|
Melting Point |
Boiling Point |
|
The temperature at which solid changes into its liquid form is considered the melting point. |
The temperature at which a liquid turns into its vapor form is considered the boiling point. |
|
The effect of external pressure on melting point depends on the specific substance and the conditions under which it is being tested. |
The boiling point is directly affected by the eternal pressure. |
|
It is used to define the characteristics of substances in the solid state. |
It is used to define the characteristics of substances in a liquid state. |
|
Ionic compounds usually have a higher melting point due to the stronger interaction between the atoms. |
The structure of a substance highly affects the boiling point. |
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How are Boiling and Melting Points Determined?
Melting and boiling points are usually found through simple lab methods. To check the melting point, a small amount of the solid is heated slowly, and the temperature at which it starts turning into a liquid is noted. For boiling points, a liquid is heated until it starts forming bubbles and changes into gas. Tools like a thermometer and heating setup are used to measure the exact temperature. These values help identify substances and check their purity as pure materials have sharp and fixed melting or boiling points.
Factors affecting the Boiling and Melting point?
The melting and boiling points of a substance can change due to important factors. First, stronger forces between particles (like hydrogen bonds or ionic bonds) usually lead to higher melting and boiling points. Second, the size and shape of molecules matter; bigger or heavier molecules often need more heat. Third, if there are impurities, they can either lower the melting point or raise the boiling point. Lastly, pressure plays a key role, especially for boiling. For example, water boils at a lower temperature in hill stations because the air pressure is lower.
Real Life Applications and Experiences
Knowing the melting and boiling points of substance is useful in everyday life and in science. In the kitchen, we see these changes while boiling water or melting butter. In labs, these points help identify unknown substances or check how pure they are. Industries like food, medicine, and cosmetics rely on this information to make sure products are made safely and work properly. Even weather and altitude can affect boiling points, which is why cooking instructions sometimes vary by location.
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FAQ
Why do covalent compounds have low melting and boiling point?
Covalent compounds have weaker bonds with the less intermolecular force of attraction. As a result, they require a very small amount of energy to break the bond due to which the melting and boiling points of covalent compounds are low.
Why do carbon compounds have low melting and boiling point?
The carbon compounds are usually covalent with less force of attraction between them. Therefore, they have low melting and boiling point.
Is there a relationship between melting and boiling points?
There is no specific relationship between melting and boiling point but the higher melting and boiling point of a substance indicate the non-covalent nature of the compound.
On which factors do melting and boiling point depend?
The melting and boiling points of a substance depend upon the strength of the bond, intermolecular forces, shape, and size of the molecule.
What causes high melting and boiling points?
Stronger bonds, larger shapes, and sizes are some of the causes behind the high melting and boiling point of any substance.