P- B-H Cycles =) Flashcards
Enthalpy of hydration of Mg2+ ions: −1920
Enthalpy of hydration of Na+ ions: −406
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Explain why there is a difference between the hydration enthalpies of the magnesium and sodium ions. (2)
- Mg2+ - smaller + ↑ charged
- attracts H2O ↑ strongly
Enthalpy of hydration-
Mg2+ (g): -1920
Ca2+ (g): -1650
Suggest why the value for Ca2+ is less exothermic than that of Mg2+. (2)
- Ca2+ - larger ion
- weaker attraction to (Oδ- in) water
Define the term electron affinity for chlorine. (2)
- enthalpy change for formation of 1 mole of Cl- ions from chlorine atoms
- atoms & ions in gaseous states
Suggest why aluminium hydroxide is insoluble in water. (1)
- high lattice enthalpy
- // strong covalent bonds
Define bond dissociation enthalpy as applied to chlorine. (2)
- enthalpy change to break the bond in 1 mol of Cl2 molecules
- to form 2 mols of gaseous chlorine atoms
A calculation of the enthalpy of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value than the value calculated (-869kJmol-1).
Explain this difference. (2)
- AgI contains covalent character
- forces holding the lattice tgt are stronger
Give an equation that represents the process when the standard enthalpy of atomisation of iodine is measured. (1)
1/2 I2 (s) –> I (g)
1 mol of gaseous atoms formed!
The enthalpy of lattice formation for caesium iodide obtained by experiment is -585kJmol-1.
The value obtained by calculation using the perfect ionic model is –582 kJmol–1.
Deduce what these values indicate about the bonding in caesium iodide. (1)
almost perfectly ionic
Units for molar enthalpy of vaporisation (∆Hvap)
kJmol-1
Explain why the enthalpy of hydration of fluoride ions is more negative than the enthalpy of hydration of chloride ions. (2)
- F- ions are smaller/ higher charge density
- stronger attraction to δ+ H
