Melting Point

The Melting Process

Melting refers to a change in the phase of a substance from a solid-state to a liquid state. This is a phase transition phenomenon. It means that, in this procedure, a substance is converted from one state of matter (solid) to the other (liquid). Melting and otherwise, fusion is a physical condition that involves the change of a substance from a solid-state to a liquid state. This occurs whenever the internal energy of the solid increases, generally via the application of heat or pressure, which raises the temperature of an object to the melting point.

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What is Latent Heat?

It is the energy absorbed or released by a substrate throughout a change in its physical state (phase) that takes place without modifying its temperature. The heat which is associated with the melting of a solid or the freezing of a liquid is called the latent heat of fusion, and the heat that is associated with the vaporization of a liquid or solid or even the condensation of vapour is called the latent heat of vaporization.

Latent heat is usually defined as the amount of heat required in units of joules or calories, per mole or unit mass of the substance currently experiencing a change of state of matter.

Latent heat is linked with procedures other than changes in the solid, liquid, and vapour states of a specific element. Almost all solids exist in different crystalline modifications, and the transformations between them usually involve the absorption or evolution of latent heat. 

How Does Melting Occur?

  • Almost all solids are assembled or packed in a rigid crystal lattice with strong intermolecular forces of attraction.  When the heat passes, the internal binding energy of the crystal lattice will be overcome by the heat energy, and the intermolecular attraction forces get weakened.

  • This weakening of intermolecular forces of attraction leads to instability in the crystal lattice. The molecules of the solids tend to separate from each other and begin moving in different directions. The instability of the crystal lattice triggers the melting of a solid substance.

  • According to the accepted melting theory, when the temperature of the substance starts to increase as a result of heat supplied or increased pressure, the molecules of the substance begin to vibrate at their places. When the amplitude (or distance covered) of the vibration surpasses the interatomic distance of the material, it causes vibrational instability and induces the substance to melt.

Melting Point 

The melting point is the temperature of the solid at which it transforms its physical state of matter from solid-state to liquid state at atmospheric pressure. The two phases of the solid and liquid state remain at equilibrium at the melting point. This means that at the melting point both the solid-state and the liquid state exist concurrently.  The melting point of the substance also changes depending on the change in atmospheric pressure.

Example Questions 

Question 1) What is the melting point of metals? What are the melting temperatures of metals found commonly?

Answer) The melting point of a material is the temperature at which it changes its physical state from solid to liquid at atmospheric pressure. At the melting of a substance, it’s solid and liquid states are actually in equilibrium. The melting point of a substance depends on the pressure and is usually specified as the standard pressure. The melting points of all metals also depend on their physical and chemical properties which involve their intermolecular forces of attraction, and hence the values are different for different metals.

The melting points of common metals are: 

Bronze: 913 °C

Brass: 927 °C

Copper: 1083 °C

Iron: 1538 °C

Steel: 1371 °C

Nickel: 1452 °C

Gold: 1064 °C

Silver: 961 °C

Question 2) Why is the heat energy required to melt a solid? 

Answer) Heat energy is needed to melt the solid because the heat energy increases the kinetic energy of the particles, which is sufficient to break the attraction or bond between the particles and to make them move faster. As a result, the state of matter is transformed from solid-state to a liquid state, or we can say that it is a conversion of solid to liquid.

FAQ (Frequently Asked Questions)

Question 1) What is the Difference Between Melting and Fusion?

Answer) Melting is described as a process in which the solid changes the liquid state without even any change in temperature. This melting process is also known as a fusion process. The amount of heat needed to transfer 1 kg of solid to its liquid state at atmospheric pressure without even a temperature change (i.e. at its melting point) is named the latent melting heat.

Change of the solid-state to the liquid state is called fusion solid to liquid, whereas the minimum temperature at which the solid-state shifts to the liquid state at the normal atmospheric pressure is termed the melting point.

Fusion, in the context of nuclear reactions, is a process where two or more objects or species combine to form a single species. It is used in relation to nuclear reactions of two types: nuclear fission and nuclear fusion. Thus, in nuclear fusion, two or more nuclei of lighter atoms combine to form a nucleus of heavier atoms.

This is the fusion and melting difference.

Question 2) Explain the Latent Heat of Fusion.

Answer) Latent heat of fusion 

  • After the substance has risen to the temperature of the melting point, the heat added after this point does not raise the temperature of the substance but is used to completely change the phase of the substance from solid-state to a liquid state.

  • The heat supplied to the solid from its melting point is the latent heat of fusion. It is defined as the heat energy required to fully transform 1 kg of solid to liquid at atmospheric pressure. The term latent, which means hidden, is just used as this heat is subtly hidden because it does not seem to appear on a temperature scale.