Final answer:
Crystalline solids have a high and fixed heat of fusion due to strong and uniform attractive forces holding their particles in a well-ordered arrangement. Their melting point and enthalpy of fusion reflect the strength of these forces, with stronger forces resulting in higher values. The melting process occurs at a constant temperature until the entire solid has melted.
Step-by-step explanation:
Do crystalline solids have a high and fixed enthalpy (heat) of fusion? Yes, crystalline solids tend to have a high and fixed heat of fusion because they consist of a well-ordered arrangement of atoms, molecules, or ions with strong and uniform attractive forces between them. The enthalpy of fusion is the amount of energy required to change a solid into a liquid at its melting point without a change in temperature.
The melting point and enthalpy of fusion are indicative of the strength of these forces—solids with stronger attractive forces will have higher melting points and higher enthalpies of fusion. For example, ice, which has strong hydrogen bonds between water molecules, requires a relatively high amount of energy to melt, resulting in a high enthalpy of fusion compared to methane (CH4), which has weaker intermolecular forces.
The distinct melting point of a crystalline solid occurs because every unit within the crystal is bound by the same strength of forces. When energy is added, as heat, the temperature of the solid remains constant until all of the solid has transitioned to the liquid phase, which is known as the melting process.