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[OBSELETE] Edexcel - A Level Chem > Topic 13 > Flashcards

Topic 13 Flashcards

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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)
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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
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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
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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
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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
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6
Q

What are the steps for constructing a Born-Haber cycle?

A
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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:

  1. The ions are in contact with each other
  2. Ions are perfectly spherical
  3. There is an even distribution of charge and no covelent characteristics
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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
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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
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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

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11
Q

Explain this diagram

A
  • The high charge density of the Cation
  • An Anion with a high charge and big size
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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

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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
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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
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15
Q

What are the calculations involving the enthalpy of hydration and enthalpy of the solution?

A
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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
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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
Q

How do you find the temperature from the entropy of the system?

A
26
Q

What is does this diagram show?

A

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
Q

What is Gibbs free energy?

A
  • 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
Q

What is the formula for Gibbs free energy?

A

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
Q

How do you find temperature from enthalpy change

A
30
Q

How does temperature effect a reactions feasibility?

A
31
Q

What does a low Gibbs value mean for the equilibrium constant?

A
  • 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
Q

What does a high Gibbs value mean for the equilibrium constant?

A
  • 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
Q

What does is mean if the equilibrium constant is very large?

A
  • If K becomes so large
  • Gibbs free energy would become so negative
  • Meaning that reactants are almost entirely converted to completion
34
Q

What is the formular for finding Gibbs from Equilibrium constant?

A
35
Q

What is second electron affinity?

A
  • The enthalpy change when 1 mole of gaseous 2 ions
  • Are made from 1 mole of gaseous 1 ions
36
Q

What is an extended born haber cycle

A

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
Q

What is polarisablity of small cations?

A
  • 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
Q

What is required for a substance to be dissolved?

A
  • 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
Q

What does effect does charge have on the enthalpy charge of hydration?

A
  • 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
Q

What does effect does size have on the enthalpy charge of hydration?

A
  • Smaller ion has higher charge density
  • Stronger water molecule attraction
  • Meaning stronger enthalpy of hydration
  • SMALLER ION = GREATER ENTHALPY OF HYDRATION
41
Q

Why can a reaction be feasible if its enthalpy is endothermic?

A
  • 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
Q

How can equalibrium constants be calculated from gibbs?

A

[OBSELETE] Edexcel - A Level Chem (27 decks)

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