Question

11 b.Explain the different enthalpy changes in phase transformation.​

Answer 1

Answer:

Explanation:

Phase changes involve energy changes. Ice, for example, requires heat for melting. Normally this melting takes place at constant pressure (atmospheric pressure) and during phase change, temperature remains constant (at 273 K). H2O (s) → H2O (l); ΔfusHΘ = 6.00 kJ mol-1 Here Δfus HΘ is enthalpy of fusion in standard state. If water freezes, then process is reversed and an equal amount of heat is given off to the surroundings, that is ΔfreezeHΘ = -Δfus HΘ This enthalpy is called enthalpy of fusion or molar enthalpy of fusion. Δfus HΘ = HΘliquid - HΘsolid Melting of a solid is endothermic, so all enthalpies of fusion are positive. Amount of heat required to vaporize one mole of a liquid at constant pressure and temperature is called its enthalpy of vaporization or molar enthalpy of vaporization. Here constant temperature is its boiling point, TP. In case of water vaporization H2O (l) → H2O (g); ΔvapHΘ = + 40.79 kJ mol-1 Sublimation is a direct conversion of a solid into its vapour. Solid CO2 or 'dry ice' sublimes at 195 K with ΔsubHΘ = 25.2 kJ mol-1, napthalene sublimes slowly and for this ΔsubHΘ = 73.0 kJ mol-1. Because enthalpy is a state property, the enthalpy of sublimation can be expressed as ΔsubHΘ = ΔfusHΘ + ΔfusHΘ.Read more on Sarthaks.com - https://www.sarthaks.com/602186/explain-enthalpy-changes-during-phase-transformations

Answer 2

Answer:

Enthalpy can be represented as the standard enthalpy, ΔHo. This is the enthalpy of a substance at standard state. ... Standard Enthalpy of Sublimation (ΔHsubo) is the energy that must be supplied as heat at constant pressure per mole of molecules converted to vapor from a solid.