✅13 - Energetics II
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What is standard lattice energy?
The energy change when one mole of ionic solid is formed from its gaseous ions under tankard conditions.
What is the equation for standard lattice energy for NaCl?
Na+(g) + Cl-(g) —-> NaCl(s)
What are the factors affecting the magnitude of lattice enthalpy?
The charge on the ion The amount of cation-anion interactions in the molecule The distance between the centres of the cations and the anions
What is the standard enthlapy change of atomisation?
The enthlapy change when one mole of gaseous atoms is formed from an element in its standard state.
What is the equation for the atomisation of Na?
Na(s) —-> Na(g)
What is electron affinity?
The first energy change is the change when each atom in one mole of atoms in the gaseous state gains an electron to form a -1 ion
What is the equation for the first electron affinity of Chlorine?
Cl(g) + e- —-> Cl-
Which enthlapy change goes on the bottom of the Born Haber cycle?
The enthlapy change of formation
What is experimental lattice energy?
That calculated from a Born-Haber cycle
What is theoretical lattice energy?
The value found from X-ray crystallography
What are the assumptions made with theoretical lattice energy?
The ions are in contact with one another The ions are perfectly spherical The charge on each ion is evenly distributed around the centre so that each ion can be considered as point charges
What does an agreement between theoretical and experimental lattice energies indicate?
That the ionic model is good for the compound, so it has good ionic character.
What does a significant difference between vales for experimental and theoretical lattice energies indicate?
That the compound has significant covalent character
When as an ion polarised?
When the electrons are pulled towards the cation and the distribution of electron density is distorted
What factors increase polarisation?
A high charge and small size of the cation A high charge and large size of the anion
Which ions are polarised most easily?
Anions with a large charge and large size
What is the enthalpy change of solution?
The energy change when one mole of an ionic solid dissolves in water to form an infinitely dilute solution
Upon dilution, how do the ions move?
They move apart (endothermic) and become more hydrated (exothermic)
How is the value for enthalpy change of solution found?
The value cannot be found experimentally so is found by a process of extrapolation.
What is the point of infinite dilution?
The point where further dilution has no measurable effect on the enthalpy change of solution.
What is the enthalpy change of hydration?
The enthalpy change when one mole of an ion in a gaseous state is completely hydrated in water
In practice, when has complete hydration occurred?
When the solution formed is of infinite dilution
What is ion-dipole interaction?
The interaction as a result of the attraction between the delta - oxygen atom of the water molecule and the cation.
What are the factors affecting the magnitude of hydration enthalpy?
The charge on the ion The ionic radius