Resources | Subject Notes | Physics
This section describes the processes of melting and boiling, focusing on how energy input affects these changes without a change in temperature.
Melting is the process by which a solid changes into a liquid. This occurs when the solid is heated.
When a solid is heated, the particles within it gain kinetic energy and vibrate more vigorously. The melting point is the specific temperature at which the particles in the solid gain enough kinetic energy to overcome the intermolecular forces holding them in a fixed lattice structure. At this point, the solid transitions into a liquid.
The energy required to melt a substance is called the latent heat of fusion. This energy is absorbed by the solid and does not cause a change in temperature. Instead, it is used to break the bonds between the particles.
The amount of energy (Q) required to melt a substance is given by the equation:
| Quantity | Formula |
|---|---|
| Mass of substance (m) | kg |
| Latent heat of fusion (Lf) | $J/kg$ |
| Energy input (Q) | $Q = mL_f$ |
Boiling is the process by which a liquid changes into a gas (or vapour). This occurs when the liquid is heated.
The boiling point is the specific temperature at which the vapor pressure of the liquid equals the surrounding atmospheric pressure. At this point, the liquid molecules have enough kinetic energy to escape from the liquid phase and enter the gaseous phase.
Similar to melting, the temperature of the liquid remains constant during boiling, even though energy is being added. This energy is used to overcome the intermolecular forces holding the liquid molecules together, allowing them to transition into the gaseous state. The energy required for this phase change is the latent heat of vaporization.
The energy required to boil a substance is called the latent heat of vaporization. This energy is absorbed by the liquid and does not cause a change in temperature. It is used to overcome the intermolecular forces and allow the molecules to escape into the gaseous phase.
The amount of energy (Q) required to boil a substance is given by the equation:
| Quantity | Formula |
|---|---|
| Mass of substance (m) | kg |
| Latent heat of vaporization (Lv) | $J/kg$ |
| Energy input (Q) | $Q = mL_v$ |
Evaporation is a type of boiling that occurs at a temperature below the boiling point of a liquid. It happens when some of the liquid molecules gain enough kinetic energy to escape into the gaseous phase.
Even at temperatures below the boiling point, liquid molecules are constantly gaining kinetic energy. Some of these molecules will have enough energy to overcome the intermolecular forces and escape into the air as a gas. The energy required for evaporation is the latent heat of vaporization.
Several factors can affect the rate of evaporation, including: