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AQA Chemistry (AS Level) > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What is enthalpy

A

Heat energy

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2
Q

What is entropy

A

Measure of chaos/disorder in substances and reactions.

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3
Q

Enthalpy of formation

A

The enthalpy to produce 1 mol of a compound from its constituent elements under standard conditions

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4
Q

Enthalpy of combustion

A

The enthalpy to burn 1 mol of a compound under standard conditions.

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5
Q

Enthalpy of atomisation

A

The enthalpy to produce 1 mol of gaseous atoms from an element in it’s standard state.

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6
Q

Enthalpy of dissociation

A

The enthalpy when all the bonds of the same type in 1 mole of gaseous molecules are broken.
e.g. Cl2(g) -> 2CL(g)

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7
Q

Enthalpy of ionisation

A

The enthalpy to remove 1 mole of electrons from 1 mole of gaseous atoms, producing 1 mole of gaseous 1+ ions.

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8
Q

Enthalpy of electron affinity

A

The enthalpy required to add 1 mole of electrons to 1 mole of gaseous atoms, producing 1 mole of gaseous 1- ions.

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9
Q

Enthalpy of lattice dissociation

A

The enthalpy required to completely dissociate an 1 mole of an ionic solid compound to produce its gaseous ions under standard conditions.

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10
Q

Enthalpy of lattice formation

A

The enthalpy required to form 1 mole of a solid ionic compound from its gaseous ions under standard conditions.

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11
Q

Enthalpy of solution

A

Enthalpy required to dissolve 1 mole of solute completely in solvent so that no further enthalpy change occurs on further dilution.

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12
Q

Enthalpy of hydration

A

Enthalpy required to turn 1 mole of gaseous ions, into 1 mole of aqueous ions.

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13
Q

Which enthalpies are exothermic.
Why?
What arrow shows this on BH cycles?

A
  • Formation, Electron affinity 1, Lattice Formation.
  • Loses energy to surroundings whilst undergoing
    reaction.
  • Downward arrows
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14
Q

Which enthalpies are endothermic?
Why?
What arrows show this?

A
  • Atomisation, Ionisation, Dissociation, Hydration, Electon Affinity 2, Lattice Dissociation.
  • Absorbs energy from surroundings so goes up in enthalpy
  • Upward arrows
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15
Q

What two factors affect the enthalpy of something?

A
  • Atomic radius

- Atomic charge

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16
Q

Explain the trend down periodic groups.

A

As we go down, atomic radius increases.
G1 - smallest radii
G7 - largest radii

17
Q

Explain the importance of atomic radius in terms of enthalpy.

A

Positively ions suited to smaller radii;
stronger attraction (electrostatic) between nuclei - outer electron - easier to attract.
Negative ions suited to larger radii;
weaker attraction (electrostatic) to outer electron - easy to lose.
Small positive ion with large negative ion creates a strong lattice (requires lot of enthalpy to dissociate/form)

18
Q

Explain the trend across periods.

A

As we go across, nuclear charge increases; number of protons and electrons.

19
Q

Explain the importance of nuclear charge.

A 
Higher charge (on +ion), higher electrostatic force to -ion, greater bond strength; more enthalpy to form/dissociate.
Lower charge (on -ion), higher electrostatic force to +ion, greater bond strength; more enthalpy to form/dissociate.
20
Q

What is the perfect ionic model?

A

PIM - theoretical calculation of enthalpy; counts all ions as perfect spheres - perfect bond.

21
Q

How is a BH value different to a PIM value?

A

BM value counts covalent characters; when ions have a strong electrostatic force to each other, becomes partly covalent due to strength; PIM value suggests perfect spherical structure w/o covalent character.
Cov. Character increases lattice enthalpy.

22
Q

What factors influence covalent characters?

A
  • Large difference in atomic radii

- Greater nuclear charges.

23
Q

What is the formation enthalpy equation?

A

H = H(prod) - H(reac)

24
Q

Enthalpy of vaporisation

A

Enthalpy required to produce 1 mole of gaseous ions from 1 mole of aqueous ions.

25
Q

How do Enth.Hyd, Enth.Sol and Enth.LatF work together?

A

(-)LatF + Hydr = Sol

26
Q

Why is Electron affinity 1 exothermic?

A

Adding an electron to an electron defficient atom is easy; ATTRACTION of nuclei to outer shell STRONG, requires little energy - more ENERGY RELEASED than required.

27
Q

Why is Electron affinity 2 endothermic?

A

2 electrons in a sub-orbital; electron-repulsion from previosuly added electron, REQUIRES more energy than it releases.

28
Q

How does solubility fluctuate depending on the compound?

A

Molecules/compounds with high electrostatic strength would take much more enthalpy of solution to dissolve.

  • charge density affects strength
  • covalent characters if charge densities high.

AQA Chemistry (AS Level) (11 decks)

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