Question

Enthalpy of atomisation
Enthalpy of fusion

Answer 1

Hint :A thermodynamic system's enthalpy is defined as the sum of the system's internal energy and the product of its pressure and volume. It is a state function that is employed in many chemical, biological, and physical tests under constant pressure, which is readily given by the huge ambient environment.

Complete Step By Step Answer:
Enthalpy of atomization
The enthalpy of atomization is the enthalpy change that occurs when all atoms in a chemical compound are completely separated. The symbol $ {{\mathbf{\Delta }}_{{\mathbf{at}}}}H\;or\;{\mathbf{\Delta }}{H_{{\mathbf{at}}}} $ is frequently used to indicate this. Because atomization breaks all bonds in the molecule while forming none, enthalpies of atomization are always positive. At 298.15 K (or 25 degrees Celsius) and 100 kPa, the related standard enthalpy is known as the Standard enthalpy of atomization, $ {\Delta _{at}}Ho/(kJ\,mo{l^{ - 1}}). $
When a compound's bonds are broken and the component atoms are divided into individual atoms, the enthalpy of atomization is the amount of enthalpy change. The symbol for enthalpy of atomization is $ {{\mathbf{\Delta }}_{{\mathbf{at}}}}H\;or\;{\mathbf{\Delta }}{H_{{\mathbf{at}}}} $ . The sum of the HO–H and H–O bond dissociation enthalpies, for example, is the enthalpy change of atomization of gaseous $ {H_2}O $ . The enthalpy of atomization of an elemental solid is the same as the enthalpy of sublimation of any elemental solid that evaporates into a monatomic gas. Because the conventional enthalpy change is predicated only on the creation of one mole of gaseous atoms, only half a mole of molecules will be required to convert a diatomic element to gaseous atoms.
Enthalpy of fusion
The change in enthalpy of a substance, also known as (latent) heat of fusion, occurs when energy, often heat, is applied to a specified quantity of the substance to change its state from solid to liquid under constant pressure. For example, when 1 kilogram of ice is melted at $ 0^\circ C $ under a variety of pressures, 333.55 kJ of energy is absorbed with no change in temperature. When a material turns from liquid to solid, the heat of solidification is equal and opposite.
The 'enthalpy' of fusion is a latent heat because the heat energy required to transform a solid to a liquid at atmospheric pressure is latent heat of fusion since the temperature remains constant during the process. The enthalpy change of any quantity of substance as it melts is known as the latent heat of fusion. The specific heat of fusion is the enthalpy change per quantity of material in moles when the heat of fusion is linked to a unit of mass, whereas the molar heat of fusion is the enthalpy change per quantity of material in moles.

Note :
The internal energy of the liquid phase is higher than that of the solid phase. This means that energy must be provided to a solid to melt it, and energy must be withdrawn from a liquid to freeze it, because the molecules in the liquid have weaker intermolecular interactions and hence have a larger potential energy (a kind of bond-dissociation energy for intermolecular forces). When liquid water is chilled, its temperature gradually decreases until it reaches slightly below the freezing point of $ 0{\text{ }}^\circ C $ . While the water crystallises, the temperature stays at the freezing point. The temperature of the water continues to drop once it is entirely frozen.