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

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

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
Q

Are lattice enthalpies always endo or exo thermic

A

Exothermic

26
Q

Why are lattice enthalpies always exothermic

A

Heat is released when ions come together the form ionic bonds

27
Q

If the lattice enthalpy is more exothermic, is the ionic bonding weaker or stronger

28
Q

What are the 2 factors that affect the lattice enthalpy

A
  • The size of the ions
  • The charge on the ions
29
Q

How does the size of the ions affect the lattice enthalpy

A

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
Q

How does the charge on the ions affect the lattice enthalpy

A

Greater the charge, the greater their charge density, so the stronger the attraction between the ions, and the more exothermic the lattice enthalpy

31
Q

What is the name of the lattice enthalpy cycles

A

Born-Haber cycle

32
Q

Going down a group do the lattice enthalpies become more or less exothermic

A

Less exothermic

33
Q

Why do lattice enthalpies become less exothermic going down a group

A
  • 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
Q

Do lattice enthalpies become more or less exothermic across a group

A

More exothermic

35
Q

Why do lattice enthalpies become more exothermic across a group

A

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