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Chemistry (Physical) > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What is enthalpy of formation

A

The enthalpy change when one mole of a compound is formed from its elements, with all reactants and products in their standard states under standard conditions

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2
Q

Is enthalpy of formation exo or endothermic

A

It is exothermic

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3
Q

What is enthalpy of atomisation

A

Enthalpy change for the formation of one mole of gaseous atoms from elements in their standard state

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4
Q

What is the equation for enthalpy of atomisation of Na (state what type of bond is broken)

A

Na(s) —> Na(g)
( metallic bonds broken

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5
Q

What is the enthalpy of atomisation equation for Cl (state what type of bond is broken)

A

1/2Cl2(g) —> Cl(g)
Intermolecular forces broken

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6
Q

What is first ionisation energy

A

X(g) —> X+ + e-

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7
Q

Is ionisation energy an exothermic or endothermic reaction

A

It is endothermic

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8
Q

Why is ionisation energy endothermic

A

Because energy is required to overcome the electrostatic force of attraction between the nucleus of the atom and the electron being removed

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9
Q

Explain why successive ionisation energies are more endothermic

A

It is harder to remove an electron from a more positive ion
Electron that is being removed is closer to the nucleus therefore more strongly attracted

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10
Q

What is the equation for 1st elctron affinity

A

X(g) + e- –> X-(g)

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11
Q

Is 1st electron affinity exo or endothermic

A

Exothermic

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12
Q

Explain why 1st electron affinity has a negative ΔH

A

There is a net attractive force between the nucleus of the atom and the electron added therefore energy is released

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13
Q

What is the equation for second electron affinity

A

X-(g) + e- –> X2-(g)

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14
Q

Explain why second electron affinity and and successive energy affinities are endothermic

A

Repulsion between the negative ion and electron
Therefore energy is required to overcome repulsion

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15
Q

State a trend in successive electron affinities

A

They get progressively more endothermic

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16
Q

What is Lattice dissociation

A

The standard enthalpy change for the dissociation of one mole of a solid ionic lattice into its gaseous ions

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17
Q

What is the general formula for lattice dissociation

A

MX(s) —> M+(g) + X-(g)

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18
Q

What is the symbol for lattice dissociation

A

ΔHL

19
Q

What is the symbol for electron affinity

A

ΔHea

20
Q

What is the symbol for ionisation energy

A

ΔHi

21
Q

What is the symbol for enthalpy of atomisation

A

ΔHat

22
Q

What is the symbol for enthalpy of formation

A

ΔHf

23
Q

What is enthalpy of solution

A

Enthalpy change for: MX(s) —-> M+ (aq) + X-(aq)

24
Q

What is enthalpy of hydration

A

Enthalpy change for X+/-(g) ——> X+/-(aq)

25
Q

Draw a solution Hess cycle for Nacl

A

-

26
Q

What is in the top left of a solution Hess cycle

A

Compound in solid state

27
Q

What is at the bottom of a solution Hess cycle

A

Ions in gaseous state

28
Q

What is in the top right of a solution Hess cycle

A

Ions in aqueous state

29
Q

What does the arrow going from the compound to gaseous ions represent in a solution Hess cycle

A

Enthalpy of lattice dissociation

30
Q

What do the arrows going from gaseous ions to aqueous ions represent in a solution Hess cycle

A

Enthalpy of Hydration

31
Q

What does the arrow going from the solid ionic compound to aqueous ions represent in a solution Hess cycle

A

Enthalpy of solution

32
Q

What does the arrow going from the solid ionic compound to aqueous ions represent in a sol

A
33
Q

What is the equation for enthalpy of solution

A

Enthalpy of lattice dissociation + Enthalpy of hydration positive ion + enthalpy of hydration of negative ion

34
Q

What affects the value of enthalpy of lattice formation/dissociation

A

Smaller & highly charged ions have a higher charge density - giving stronger electrostatic force of attraction between oppositely charged ions
Gives more exo value for formation
Gives more enforcing value for dissociation

35
Q

What affects the value of enthalpy of hydration for positive ions

A

The force of attraction between the delta negative O of water, and the positive ion

36
Q

What causes a stronger force of attraction between a delta negative oxygen on a water molecule and a positive ion (how does it affect the value of enthalpy of hydration)

A

Smaller more positive ions will have a higher charge density
Will attract delta H oxygen on H2O stronger
Which gives a more exothermic value for enthalpy of hydration

37
Q

What affects the value of enthalpy of hydration for negative ions

A

The attraction between the delta positive H on a H2O molecule and the negative ion

38
Q

What affects the attraction between delta positive H on a water molecule and a negative ion (how does it affect the value of enthalpy of hydration)

A

Smaller more negative ions will have a larger charge density
This will attract the delta positive H on the H2O stronger
This gives a more exothermic value for enthalpy of hydration

39
Q

When is covalent character more prevalent

A

The more charge dense the positive ion is, as well as when there is a larger or more negative, negative ion.
(n+ more polarising, n- more polarisable)

40
Q

When does the most covalent character occur

A

When we have small, highly positive ions are bonded to highly negative ions

41
Q

What does the perfect ionic model assume

A

Assumes that the ions are perfect spheres (no covalent character)

42
Q

When will the born barber value for enthalpy of lattice F/D be similar to the value from the PIM equation

A

When there is no/little covalent character

43
Q

If there is covalent character present, how will the born haber value differ from the P.I.M value for lattice enthalpy of F/D

A

The value will typically be larger
Either more -ve for lattice enthalpy of dissociation
Or more +ve for lattice enthalpy of formation

44
Q

What is bond enthalpy

A

The amount of energy required to break one mole of a specific covalent bond in the gas phase

Chemistry (Physical) (10 decks)

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