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Hidden Energy in Thermodynamics: Do you know why energy doesn't change the temperature during melting?
Melting processes are everywhere around us. Whether it's snowflakes melting into water or ice cubes disappearing into drinks, the process of melting is accompanied by curious scientific phenomena. The principles of thermodynamics involved in this process provide us with a deep understanding of how energy is converted between states of matter. In thermodynamics, this energy conversion is called "heat of fusion", which is the heat required to change to a liquid state, but there is a special feature, that is, the temperature remains constant during the melting process.
Definition and characteristics of heat of fusion
The heat of fusion, or latent heat, is the heat absorbed by a substance when it melts without causing a change in its temperature. When a solid changes to a liquid, the temperature of the substance remains constant although the external heat supply increases. This phenomenon occurs because during the melting process, the molecular structure of the substance changes, but the energy is used to overcome the attraction between the molecules instead of increasing the temperature.
"The heat of fusion is the energy required when a substance changes from a solid state to a liquid state. At this stage, the distance and motion changes between molecules are the key to driving this process."
Take water as an example. When an ice cube (0°C) begins to melt, it needs to absorb about 333.55 kJ of heat, while the temperature of the water remains at 0°C throughout the process. This is because during this process, thermal energy is used to increase the kinetic energy of the molecules, which breaks the mutual bonds of the solid structure. Only after the ice has completely transformed into water does the added heat gradually increase the temperature of the water.
The effects and exceptions of latent heat
Latent heat is not limited to the melting of water, the same principle applies to other substances. For example, under certain pressures and temperatures, the heat of fusion of helium (He) is even negative, which means that helium needs to absorb heat energy when it solidifies. This anomaly has triggered in-depth research by scientists. The characteristics of these latent heats indicate that different substances have different demands and releases of thermal energy when they change states.
"The melting process of helium-3 and helium-4 is significantly different from the melting of traditional substances, allowing people to have a deeper understanding of low-temperature physics."
Application of fusion heat
Heat of fusion has applications in daily life and scientific research. In chemistry, the heat of fusion can be used to predict the solubility of a substance in a solution. In an ideal solution, the mole fraction of solute is closely related to the heat of fusion and the melting point of the solid. For example, when dissolving acetaminophen in water, the properties of the heat of fusion can be used to more accurately calculate solubility, which is not only crucial for chemical experiments, but also of great significance to the pharmaceutical industry.
Explanation of the melting process
When we heat a solid to its melting point, the molecules in the solid gain enough kinetic energy to break the interaction forces that limit their motion and enter a liquid state. In this process, the heat of fusion provides the required energy, and the temperature remains constant during this period until the solid is completely transformed into a liquid, which contains the basic laws of thermodynamics.
"The existence of heat of fusion reveals the need for and conversion of energy between states of matter, which is an integral part of physics and chemistry."
The specificity of the melting process extends beyond form to deeper scientific understanding. We realize that when a substance melts, the absorption of heat energy doesn't just make the molecules more active, but works to change their internal structure. This feature involves more than just water, so what unique changes will other substances undergo during the melting process?
