lattice Flashcards
Define enthalpy change of atomisation
When 1 mole of gaseous atoms is formed from its element in its standard state under standard conditions
So the gaseous atoms are formed from standard state elements
Define ∆Hθlatt
the enthalpy change that occurs when 1 mole of a solid ionic compound is formed from its gaseous ions *under standard conditions *
can the enthalpy change be measured directly?
No = impossible to directly isolate the gaseous ions then combine them
What enthalpy changes are included in the bon haber cycle?
Atomisation enthalpy
Ionisation enthalpy
Bond dissociation enthalpy
Electron affinity
Lattice enthalpy
Enthalpy change of formation
Define electron affinity
When 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous ions with a singly negative charge under standard conditions.
Trend of electron affinity of group 7 down the group
- Decreases
- increase energy level
- more shielding
- electrons attracted with less force
What is the exception to the gorup 7 electron affinity trend?
- F
- small atom
- high electron charge density
- electron cloud formed from F causes repulsion to the electron added
Do you think 2EA will be more or less exothermic than 1EA for oxygen? Explain
- more endothermic
- requires energy to add one electron to already negative charged ion
Is there more lattice enthalpy in MgCl or NaCl? Explain
- MgCl
- more exothermic
- Mg2+ has higher charge density than Na+
- more electrostatic forces of attraction
- MgCl more stable
define enthalpy of solution
energy absorbed or released when 1 mole of ionic solid dissolves in sufficient water to form a very dilute solution under standard conditions
will the enthalpy of solution be positive or negative?
can be either, but compound only soluble if value is negative or slightly positive
It is more stable this way
define enthalpy change of hydration
The enthalpy change when 1 mole of a specified gaseous ion dissolves in sufficient water to form a very dilute solution under standard conditions.
1 ion, not 2 ions
how do you calculate the enthalpy of solution?
ΔHθsol = ΔHθhyd - ΔHθlatt
What needs to occur for the compound to be soluble?
ΔHθsol must be –ve
Since ΔHθlatt is always –ve
ΔHθhyd must be more –ve in total than ΔHθlatt
ΔHθsol must be –ve because in this way it would be more stable
The enthalpy change of hydration of Ca2+ is –1579 kJ mol–1. Suggest why there is a big difference in the values of ∆Hhyd for Ca2+ and Cu2+.
M1: Cu2+ has a higher charge density
M2: Cu2+ forms stronger ion-dipole forces to water molecules
