In basic physical chemistry, the process of melting a solid into a liquid is also called what?

Introduction / Context:
This question belongs to the topic of phase changes in physical chemistry and physics. When a solid substance changes into a liquid, the process is known as melting, but it is also referred to by a more technical name, fusion. Understanding the different terms used for phase transitions helps you interpret textbook descriptions, heating curves, and calorimetry problems. Examinations often include such terminology based questions to ensure students are comfortable with standard scientific vocabulary.

Given Data / Assumptions:
- The question describes the process of melting, which is the change of state from solid to liquid.
- You must identify the alternative technical term for this process.
- Options provided are fusion, galvanisation, crystallisation, and evaporation.
- It is assumed that you are familiar with the basic types of phase changes and some industrial processes.

Concept / Approach:
In thermodynamics, the change of state from solid to liquid at a constant temperature is called fusion. The energy absorbed during this process is called the latent heat of fusion. Galvanisation is a surface treatment process where a metal, often iron, is coated with a layer of zinc to prevent rusting. Crystallisation is the process of forming solid crystals from a solution or melt, usually associated with the reverse of melting or with purification. Evaporation is the change of state from liquid to gas at the surface of a liquid. Therefore, only fusion correctly describes melting as a phase change from solid to liquid.

Step-by-Step Solution:
Step 1: Identify the process described in the question as melting, which is the transformation of a solid into a liquid upon heating. Step 2: Recall that in thermodynamics, the energy required to melt a solid at its melting point is called latent heat of fusion. Step 3: Recognize that the term fusion is used interchangeably with melting, particularly in phrases such as heat of fusion. Step 4: Examine the other options. Galvanisation refers to coating metal with zinc, crystallisation to formation of solid crystals, and evaporation to conversion of liquid to gas. Step 5: Conclude that fusion is the only option that matches the meaning of melting, so Fusion is correct.

Verification / Alternative check:
You can confirm this by reviewing thermodynamics and phase change chapters in physics or chemistry textbooks. They define the latent heat of fusion as the energy required to change one unit mass of a solid at its melting point into liquid at the same temperature. Graphs of heating curves also label the plateau at the melting point as the fusion phase. None of the other terms, galvanisation, crystallisation, or evaporation, are used to describe the solid to liquid transition. This consistent use of terminology confirms that fusion is the correct answer.

Why Other Options Are Wrong:
Galvanisation is a protective coating process for metals and has nothing to do with melting or phase changes. Crystallisation involves the formation of solid crystals from a solution or molten material and is often associated with solidification rather than melting. Evaporation describes the transition from liquid to gas, which is a different phase change entirely. Therefore, these terms do not match the description of melting a solid into a liquid and are incorrect in this context.

Common Pitfalls:
A common error is to confuse crystallisation with melting because both involve solids and liquids, but crystallisation refers to solid formation, not melting. Some students may also be misled by evaporation, thinking of general heating, without recognizing that evaporation involves liquids turning into gases. To avoid these mistakes, memorize the standard phase change terms: melting or fusion for solid to liquid, freezing or solidification for liquid to solid, evaporation or vaporisation for liquid to gas, and condensation for gas to liquid.

Final Answer:
The process of melting a solid into a liquid is also called Fusion.