AC15: Lattice energy Flashcards

1
Q

When heat is released, is the reaction endo or exo thermic

A

Exothermic

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2
Q

For an exothermic reaction, is the enthalpy change positive or negative

A

Negative

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3
Q

When heat is absorbed is the reaction endo or exo thermic

A

Endothermic

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4
Q

For an endothermic reaction, is the enthalpy change positive or negative

A

Positive

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5
Q

What are the standard conditions for enthalpy changes

A
  • 1 atm
  • 298 K / 25 degrees
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6
Q

Define the standard enthalpy change of a reaction

A

The enthalpy change when the number of moles of reactants shown in an equation react together under standard conditions, all reactants being in their standard states

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7
Q

Define the standard enthalpy of formation of a compound

A

The enthalpy change when 1 mole of a compound is formed form its ELEMENTS in their standard states, under standard conditions

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8
Q

Define bond enthalpy

A

The enthalpy change required to break 1 mole of bonds between 2 atoms in the gaseous state

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9
Q

Define first ionisation energy of an element

A

The energy needed to remove 1 electron from every atom in 1 mole of gaseous atoms of an element

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10
Q

Define second ionisation energy of an element

A

The energy needed to remove 1 electron from every ion in 1 mole of gaseous +1 ions of an element

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11
Q

Are ionisations endo or exo thermic

A

Endothermic

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12
Q

Why are all ionisations endothermic

A

Because energy is needed to overcome the attraction between the outer electrons and the nucleus

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13
Q

Is the first or second ionisation more endothermic

A

Second ionisation

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14
Q

Why is the second ionisation more endothermic

A

Because the number of protons remain the same but 1 less electron, so there is less repulsion between the remaining electrons, allowing them to move in closer to the nucleus, where they are more strongly attracted

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15
Q

What does Hess’s law state about the enthalpy change in a chemical reaction

A

Independent of the route taken by the reaction, provided the initial and final conditions are the same

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16
Q

Define enthalpy change of atomisation of an element

A

The enthalpy change when 1 mole of gaseous atoms of an element are formed from the element in its standard state

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17
Q

Why does aluminium have a greater enthalpy change of atomisation

A

Since the number of out shell electrons increases, so there are more electrons contributing to the metallic bond which requires more energy

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18
Q

Define the first electron affinity of an element

A

The enthalpy change when 1 electron is added to each atom in a mole of gaseous atoms of an element

19
Q

Is the first electron affinity of an element that commonly forms negative ions positive or negative

20
Q

Why is the first electron affinity of an element that commonly forms negative ions negative

A

Because the electron that is added is attracted to the nucleus more strongly than it is repelled by the other electrons

21
Q

Are second electron affinities positive or negative

22
Q

Why are second electron affinities always positive

A

Energy must be put in to overcome the repulsion between the negatively charged X- ion and the e- that is added

23
Q

Define lattice enthalpy

A

The enthalpy change when 1 mole of a sold ionic compound is formed from its gaseous ions

24
Q

What is lattice enthalpy a measure of

A

The strength of ionic bonding in a compound

25
Are lattice enthalpies always endo or exo thermic
Exothermic
26
Why are lattice enthalpies always exothermic
Heat is released when ions come together the form ionic bonds
27
If the lattice enthalpy is more exothermic, is the ionic bonding weaker or stronger
Stronger
28
What are the 2 factors that affect the lattice enthalpy
- The size of the ions - The charge on the ions
29
How does the size of the ions affect the lattice enthalpy
Smaller the ionic radii of the ion, the greater their charge density, hence stronger the attraction between the ions and the more exothermic the lattice enthalpy
30
How does the charge on the ions affect the lattice enthalpy
Greater the charge, the greater their charge density, so the stronger the attraction between the ions, and the more exothermic the lattice enthalpy
31
What is the name of the lattice enthalpy cycles
Born-Haber cycle
32
Going down a group do the lattice enthalpies become more or less exothermic
Less exothermic
33
Why do lattice enthalpies become less exothermic going down a group
- The charge on the ion stays the same but the ionic radii increases, which decreases charge density so attraction to oppositely charged ions becomes weaker
34
Do lattice enthalpies become more or less exothermic across a group
More exothermic
35
Why do lattice enthalpies become more exothermic across a group
The charge on the ion increases, and the ionic radii decreases due to the increase in nuclear charge, so there's increased attraction to other ions
36
Define enthalpy change of solution
The enthalpy change when 1 mole of a compound dissolves in a solvent
37
When an ionic solid dissolves, what are the 2 steps in the process
- Lattice breaks, endothermic reaction - Separated ions are hydrated, ion-dipole forces between ions and water, exothermic
38
Define enthalpy change of hydration
Enthalpy change when 1 mole of gaseous ions dissolve to form one more of hydrated ions
39
Is the enthalpy change of solution endo or exo thermic
Either, it depends on the balance between the lattice enthalpy and the hydration enthalpies
40
What 2 factors affect the enthalpy change of hydration of an ion
- Ionic charge - Ionic radii
41
How does ionic charge affect the enthalpy change of hydration of an ion
The greater the charge, the stronger the attraction between the ion and the water molecule, the more exothermic the enthalpy change of hydration
42
How does ionic radii affect the enthalpy change of hydration of an ion
The greater the radii, the weaker the attraction between the ion and the water molecule, so the less exothermic the enthalpy change of hydration
43
What are the bonds that form between ions and water
Ion-dipole forces