Topic 13 Flashcards
(42 cards)
1
Q
What is standard lattice energy?
A
- The energy change of a compound
- When one mole of ionic solid is formed
- From its gaseous ions
- UNDER STANDARD CONDITIONS (298K + 100kPa)
2
Q
What Factors affect lattice energy?
A
Factors that increase lattice energy
- The higher charge
- More Cation-Anion[-Cation] interactions
- The high ionic radii/ion size
3
Q
What is the standard enthalpy of atomisation?
A
- Enthalpy change when measured at
- Standard conditions (298K 100kPa)
- For one mole of gas to be produced from its element in its natural state
4
Q
What is electron affinity?
A
- The energy change
- When each atom in one mole of atoms
- In a gaseous state
- Gains an electron to form an ion
5
Q
What is the born harbour cycle?
A
A cycle that shows the energy changes in a reaction such as:
- Enthalpy change of formation
- Enthalpy change of atomisation
- First ionisation energy
- Electron Affinities
- Lattice Energy of Ionic Lattice
6
Q
What are the steps for constructing a Born-Haber cycle?
A
7
Q
What is the relationship between the theoretical and the experimental lattice energy values?
A
Theoretical values will always be higher than the experimental values because we assume:
- The ions are in contact with each other
- Ions are perfectly spherical
- There is an even distribution of charge and no covelent characteristics
8
Q
Why is there covalency in the ionic bond?
A
- The cation (+) attracts the electrons on the anion (-)
- This pulls them towards the cation distorting the electron density of the anion
- Meaning the Cation POLARISES the Anion
9
Q
Why does polarisation happen between ions?
A
- Cation (+) attracts the elections on the Anion (-)
- This pulls the electron towards the cation
- Distorting the electron density of the Anion
- Meaning the Cation polarises the Anion
10
Q
What are Fajan’s Rules?
A
Polarisation is increased:
- The high charge density of the Cation
- An Anion with a high charge and big size
11
Q
Explain this diagram
A
- The high charge density of the Cation
- An Anion with a high charge and big size
12
Q
What it the definition of enthalpy change of solution?
A
- Determines solubility
- The enthalpy change when
- One mole of ionic solid dissolves in water
- Forming an infinitely dilute solution
Made up from enthalpy of dissociation and hydration
13
Q
What is indefinite dilution?
A
- In dilution ions in a solution move apart (Endo)
- Ions also become Hydrated (Exo)
- The Exo and Endo processes affect the enthalpy change of solution referring to an infinitely dilute solution
- Where after a certain point the value won’t be affected by further dilution
14
Q
What is the definition of enthalpy change of hydration
A
- The enthalpy change
- When one mole of an ion is in a gaseous state
- Is completely hydrated by water
15
Q
What are the calculations involving the enthalpy of hydration and enthalpy of the solution?
A
16
Q
What is the effect of ionic charge on the enthalpy of hydration?
A
- The higher the charge
- The The higher the forces of attraction between the ion and the water molcules
17
Q
What is the effect of ionic radii on the enthalpy of hydration?
A
- An increase in ionic radius
- Leads to bigger ions
- With less electrostatic force of attraction between ions and water molecules
- Meaning the energy released upon hydration decreases
18
Q
What is entropy?
A
The measure of the degree of disorder or randomness of a system
A system is any chemical situation
19
Q
What happens to entropy when the state changes?
A
- The disorder increases when going from a solid to a liquid
- The disorder decrease when going from a gas to a liquid
20
Q
What happens to entropy when dissolving a solid lattice?
A
- The disorder increases when a solid dissolves
- Meaning an increase in the entropy
21
Q
What happens to entropy when there is a change in the number of moles
A
- The disorder increases when the number of moles increases
- The disorder decreases when the number of moles decrease
22
Q
What is the formula for total entropy change?
A
23
Q
What is the formula for entropy change in the system?
A
24
Q
What is the formula for entropy of the surroundings?
A
25
How do you find the temperature from the entropy of the system?
26
What is does this diagram show?
Dependent on the Gibbs Free Energy calculations
**Left to Right**
- When the reaction is endothermic and the entropy is negative the reaction isn’t feasible
- When the reaction is exothermic and the entropy is negative the reaction may feasible
- When the reaction is endothermic and the entropy is positive the reaction may be feasible
- When the reaction is exothermic and the entropy is positive the reaction is definitely feasible
27
What is Gibbs free energy?
- When there is an exothermic reaction which releases energy
- With the surroundings have been accounted for
- Any left over energy will be considered free energy
28
What is the formula for Gibbs free energy?
If Gibbs free energy is
- 0 then the reaction is **JUST feasible**
- > 0 then the reaction is feasible
- < 0 then the reaction isn’t feasible
*However just because a reaction is feasible you needs time as the rate of reaction is so slow*
29
How do you find temperature from enthalpy change
30
How does temperature effect a reactions feasibility?
31
What does a low Gibbs value mean for the equilibrium constant?
- When Gibb’s free energy is negative
- The reaction is theoretically feasible
- The equilibrium constant is greater than 1
- Meaning that products are favoured over reactants
32
What does a high Gibbs value mean for the equilibrium constant?
- When Gibbs's free energy is positive
- The reaction is not theoretically feasible
- The equilibrium constant is less than 1
- Meaning that reactants are favoured over reactants
33
What does is mean if the equilibrium constant is very large?
- If K becomes so large
- Gibbs free energy would become so negative
- Meaning that reactants are **almost entirely** converted to completion
34
What is the formular for finding Gibbs from Equilibrium constant?
35
What is second electron affinity?
- The enthalpy change when 1 mole of gaseous 2 ions
- Are made from 1 mole of gaseous 1 ions
36
What is an extended born haber cycle
A cycle that shows the energy changes in a reaction such as:
(Endothermic is Up and Exothermic is Down)
- Enthalpy change of formation
- Enthalpy change of atomisation
- First ionisation energy
- Electron Affinities
- **Lattice Energy of Ionic Lattice**
AS WELL AS
- second ionisation step forming positive ion2+ (endothermic)
- second affinity step forming negative ion 2- (endothermic)
37
What is polarisablity of small cations?
- Small cations are more polarising that larger ones
- Higher charge density in a smaller area
- Cation pulls electron towards itself
- Meaning larger anions will be pulled to the cation
- MORE POLARISATION = MORE COVALENT CHARACTER
38
What is required for a substance to be dissolved?
- Breaking of bonds (endothermic)
- New formation of bonds between solvent and substance (exothermic)
- New bonds must be the same strength or greater then those broken
- Meaning soluble substances tend to have an exothermic enthalpy
39
What does effect does charge have on the enthalpy charge of hydration?
- Larger charge = stronger attraction of water molecules
- Due to higher electrostatic attraction
- More energy released when bond is made which means they have a more exothermic enthalpy of hydration
- LARGER CHARGE = GREATER ENTALPY OF HYDRATION
40
What does effect does size have on the enthalpy charge of hydration?
- Smaller ion has higher charge density
- Stronger water molecule attraction
- Meaning stronger enthalpy of hydration
- SMALLER ION = GREATER ENTHALPY OF HYDRATION
41
Why can a reaction be feasible if its enthalpy is endothermic?
- Even though reaction is exothermic
- Changes in entropy can overcome changes in enthalpy
- Where entropy can outwieght enthalpy
- Through an increase in moles
- And enough of a change in states
42
How can equalibrium constants be calculated from gibbs?
