12B.3 Flashcards
what is the enthalpy change of a solution
it is the energy change measured at the standard condition when one mole of an ionic solid is dissolved in water to form an infinitely dilute solution
what is an infinitely dilute solution
its when there is so much water that adding any more would not cause further enthalpy change
the infinitely dilute solution can only be found by using
extrapolation
why is the quoted value for change in enthalpy of a solution infinitely dilute solution
it is very important to specify the extent of dilution when quoting a value for enthalpy change, and during dissolving the particles move apart (Endo) and they get hydrated (Exo) these two values change the dilution and affect the change of enthalpy of s solution in a complicated way so to make it easier we quote in to infinitely dilute solution
what is the enthalpy change of hydration
the energy change is measured at standard conditions when one mole of an ion in its gaseous state is fully hydrated by water
when does complete hydration occur
at intinite dilution
what is an ion-dipole interaction
it is interaction in Aq solutions between ions and polar water molecules
in interactions between positive ions and water molecules what can form
with some positive ions, mostly transitional metals there could form a dative covalent bond between the cation and one of the lone pairs of electrons in oxygen
enthalpy change of hydration values are always
negative
enthalpy change of a solution values are
negative and positive
what can form between an anion and water molecules in ion-dipole interactions
hydrogen bonds between the lone pair in the ion and hydrogen
why do 2+ ions have a more negative value of enthalpy change of hydration compared to 1 + ions
because the doubly charged ion would form a stronger electrostatic force with the negative water molecule (O) t
why doe the enthalpy change of hydration value become less negative as you go down the group
as the go down the group, the ionic radius increases so the electrostatic force between the ion and the negative water molecules would decrease so less energy is released when it’s hydrated
what is the relationship between teh charge density of a cation and the enthalpy change of hydration
as the charge density increases the enthalpy change of hydration becomes more negative
when writing an equation for the enthalpy change of hydration the gaseous ion would be on the
left
