Lattice Enthalpy Flashcards
What is lattice enthalpy?
The formation of 1 mole of an ionic lattice from gaseous ions
Bond forming, exothermic
(NOT THE SAME AS ENTHALPY OF FORMATION)
What is lattice dissociation enthalpy
The energy required to break down the lattice into it gaseous ions
Bond breaking, endothermic
What does a Born-Haber cycle do?
It is a model to allow the determination of lattice enthalpy
What is the enthalpy of atomisation of a metal?
Energy change when 1 mole of gaseous ions are formed from the element in its standard state
M(s) ——-> M(g)
Always positive as bonds are broken
What is the enthalpy of ionisation of metal?
The energy change when 1 mole of gaseous atoms loses 1 election to become 1 mole of gaseous unpositive ions
M(g) ———> M+(g) + e-
Always positive as interactions are broken
What is the enthalpy of atomisation of a non-metal?
Energy change when 1 mole gaseous atoms are formed from the non-metal in its standard state
1/2X2 (g)/(l)/(s) ———> X(g)
What is the enthalpy of electron affinity?
The energy change when 1 mole of atoms gain 1 mole of electrons in the gaseous state
X(g) + e- ———> X-(g)
Sign can vary
Can be first or second
What do the directions in the Born-Haber cycle show?
The direction of the arrows shows the sign in the reaction process
What steps are present in a MX cycle?
- lattice enthalpy
- enthalpy of formation
- atomisation of metal
- first ionisation energy
- atomisation of non metal
- first electron affinity
What steps are in a MX2 cycle?
- lattice enthalpy
- enthalpy of formation
- atomisation of metal
- first ionisation energy
- second ionisation energy
- atomisation of non metal x2
- first electron affinity x2
What steps are in a MO cycle?
- lattice enthalpy
- enthalpy of formation
- atomisation of metal
- first ionisation energy
- second ionisation energy
- atomisation of non metal
- first electron affinity
- second electron affinity
What steps are in an M2O cycle?
- lattice enthalpy
- enthalpy of formation
- atomisation of metal x2
- first ionisation energy x2
- atomisation of non metal
- first electron affinity
- second electron affinity
Why is first electron affinity exothermic, but second electron affinity is endothermic?
First electron affinity is exothermic because it involves attraction within a field of the electron for the positive nucleus. This gives out energy
O(g) + e- —-> O-(g)
Second electron affinity is endothermic because it involves bringing together two negatively charged species which repel each other. Energy is required to be taken in to overcome the repulsion
O-(g) + e- —-> O2- (g)
How is lattice enthalpy calculated form a born hater cycle?
fH - (atm metal + fieH + atm non metals + eaH)
How is enthalpy of formation calculated from a Born-Haber cycle?
fH = step 1 + step 2 +step 3 + step 4 + step 5
What is the enthalpy of hydration of an ion?
The energy change for dissolving of 1 mole of gaseous ions in water
Xn-(g) + (aq) ——> Xn-(aq)
Mn+(g) + (aq) ——> Mn+(aq)
Always negative as interactions are formed
What is enthalpy of solution?
The energy change to dissolving 1 mole of solute (solid lattice)
MX(s) ———> M+(aq) + X-(aq)
Can be either positive or negative
What can relative strengths of enthalpy changes be based on?
- CHARGE = comparison of the charges of the ions
- IONIC RADIUS = comparison of the size of the ions
- ATTRACTION = explanation to the size of the atttractive forces
These forces will be between positive and negative ions in lattice enthalpy, but will e between ions and water in enthalpy of hydration
What is the period trend for positive ions?
- Charge increase across the period
- ionic radius decreases across the period
- attraction to negative ions/water increases
- leH or hydH becomes more negative
What is the group trend for positive or negative ions?
- charge stays the same down the group
- ionic radius increases down the group
- attraction to oppositely charged ions/water decreases
- leH or hydH becomes less negative
