Chapter 23 (Part 1) Energetics Flashcards
1
Q
Lattice Enthalpy. (2)
A
- a measure of the strength of forces between the ions in an ionic solid
- the greater the lattice enthalpy, the stronger the forces
2
Q
Lattice Formation Enthalpy
A
- enthalpy change when one mole of an ionic lattice is formed from its isolated gaseous ions
- highly exothermic
- strong electrostatic attraction btw oppositely-charged ions
- always negative
3
Q
Lattice Dissociation Enthalpy
A
- enthalpy change when one mole of an ionic lattice dissociates into isolated gaseous ions
- highly endothermic
- strong electrostatic attraction btw oppositely-charged ions
- always positive
4
Q
Factors affecting lattice enthalpy
A
- charge density
- ionic radius
5
Q
Charge Density
A
- the strength of the bond between the ions of opposite charge in an ionic compound
- depends on charges on the ion & the distance btw the centres of ions when they pack to form a crystal
- greater charge = greater force = lattice energies more exothermic
6
Q
Ionic Radius
A
- smaller ionic radius = greater attraction between ions because of greater charge density
- increased lattice enthalpies, increased melting points
7
Q
Electron affinity
A
- energy change when 1 mole of electron is added to 1 mole of gaseous atom to form a negatively-charged ion
- X (g) + e- –> X- (g)
8
Q
Why is 1st EA exothermic & 2nd, 3rd etc. EA endothermic?
A
2nd EA onwards:
- electron repels the anion
- energy absorbed to overcome repulsion between electron & anion
9
Q
Steps for Simple Hess Cycle.
A
- Write out balanced H f & H LE.
- Atomise.
- Ionise. Metals must always be ionised before non-metals because electrons are needed for the non-metal.
- Ions come together to form solid.
- refer to class discussion
10
Q
Steps for constructing Born Haber Cycle.
A
- Big arrow upwards for energy (E).
- Arrow upwards = endothermic / enthalpy change +ve
- Arrow downwards = exothermic / enthalpy change -ve
11
Q
Enthalpy of atomisation.
A
- Enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state, under standard conditions.
12
Q
Bond enthalpy (ΔHBe)
A
- Energy required to break a particular covalent bond in 1 mole of molecule in a gaseous state
- 1/2 Cl2 (g) –> Cl (g)
13
Q
Carbonate anion dot-&-cross
A
- Refer to class discussion
- 2 single, 1 double
14
Q
Nitrate anion dot-&-cross
A
- Refer to class discussion
- 1 double, 1 single, 1 dative
15
Q
Explain delocalisation on carbonate & nitrate ions.
A
- pi bond on C=O & lone pairs overlaps with delocalised pi system
-anion is polarised due to attraction towards G2 cation (think of dipole) - under heating, weakest (polarised) bond breaks
