Melting Point

Matter generally occurs in three states around us – solid, liquid and gas. The change of state from solid to liquid is known as melting. Similarly, when a liquid turns into a solid state, it is freezing.

What is Melting?

Melting refers to the change of state from solid to liquid. The most common example of melting is ice. Keep ice cubes in a small bowl at room temperature. You will notice that this ice slowly turns into water. After a certain amount of time, the ice crystals completely disappear, and only water remains in this bowl.

The change of state from a solid to a liquid occurs due to the presence of hyperactive atoms. These atoms in the ice molecule gain energy and successfully escape from this cube. Such a change results in the frozen water to transform its state and turn into the liquid form.

Quick Question – 1

Q. Where Do Hyperactive Ice Atoms Derive Energy from to Escape the Ice Cube?

Ans. The ice atoms acquire energy in the form of heat when the ice cube is kept at room temperature. The atoms use this energy to escape from ice, thereby changing to its liquid form. 

Temperature Increase During Change from Solid to Liquid

Now that you understand what is melting, you would think that the temperature of ice would increase as it absorbs heat and melts. However, such is not the case. In fact, research indicates that temperature does not increase or decrease when such a change of state is underway. 

In fact, the temperature will only increase after the entire ice cube melts into water. Therefore, you can say that equilibrium exists between the liquid and solid states during such a change of state.

True or False     

Q. Water’s Temperature Decreases While Transforming Into Ice.

Ans. False. Water’s temperature remains the same while this process of change is underway. It can only increase after all water molecules have changed into ice molecules.

Understanding Melting Point

Melting point is the temperature at which solid and liquid phases of any pure material can exist in equilibrium. Beyond this point, the material experiences the conversion of solid to liquid. 

When heat is applied on any solid object, its temperature will increase to its melting point. At this point, the temperature of this material remains constant as long as it is still melting into its liquid form. After this melting is complete, any excess, residual heat will lead to a further increase in temperature for the resulting liquid.

Now that you understand what is melting point, here is a look at how pressure affects melting points.

Pressure and its Effect on Melting Point

In most cases, increased pressure increases the melting point for a material. This means that under high-pressure conditions, you would need to apply more heat to cause a material to melt. Ice is a rare exception to this rule.

When you increase pressure on ice, it lowers the melting point temperature. This happens primarily because ice shrinks when it turns into water. The same trait can also be explained using LeChatelier’s principle.

Example 1

One of the examples of change of state of matter in everyday life is that of an ice skater skating. The pressure from the skates causes the ice to melt. However, it refreezes as soon as the pressure is removed, that is, the skater moves off. 

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FAQ (Frequently Asked Questions)

1. Why Does a Solid Change Into Liquid on Heating?

Ans. Solid atoms are in an energized state, always ready to escape. When heat is applied, these atoms use this additional energy to escape its solid matter.

2. Which Liquid Turns Into Solid on Heating?

Ans. Albumin, a type of protein commonly found in eggs, turns solid when heat is applied to it. Another substance with similar traits is α cyclodextrins.

3. What is the Effect of Pressure on Melting Points?

Ans. Pressure and melting point are usually directly proportional to each other. However, in the case of ice and some other materials, increasing pressure may result in lower melting points.