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Chemistry - Mrs McDougal > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

Enthalpy of formation

A

Enthalpy change when one mole of a substance is formed from its constituent elements with all substances in their standards states

Exothermic (usually)

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2
Q

Enthalpy of combustion

A

Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in their standard states

Exothermic

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3
Q

Enthalpy of neutralisation

A

Enthalpy change when one mole of water is formed in a reaction between an acid and alkali under standard conditions

Exothermic

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4
Q

First ionisation enthalpy

A

Enthalpy change when each atom in a one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions

Endothermic

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5
Q

First electron affinity

A

Enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions

Exothermic for most non-metals

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6
Q

Second electron affinity

A

Enthalpy change when each atom in one mole of gaseous 1- atoms gains one electron to form one mole of gaseous 2- ions

Endothermic

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7
Q

Enthalpy of atomisation

A

Enthalpy change when one mole of gaseous atoms is produced from an elements in its standard state

Endothermic

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8
Q

Hydration enthalpy

A

Enthalpy change when one mole of gaseous ions become hydrated (converted to aqueous ions)

Exothermic

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9
Q

Enthalpy of solution

A

Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well seperated and do not interact with each other

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10
Q

Bond dissociation enthalpy

A

Enthalpy change when one mole of covalent bonds is broken in the gaseous state

Endothermic

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11
Q

Lattice enthalpy of formation

A

Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase

Exothermic

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12
Q

Lattice enthalpy of dissociation

A

Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase

Endothermic

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13
Q

Enthalpy of vapourisation

A

Enthalpy change when one mole of a liquid is turned into a gas

Endothermic

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14
Q

Enthalpy of fusion

A

Enthalpy change when one mole of a solid is turned into a liquid

Endothermic

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15
Q

What does a gap between experimental and theoretical lattice enthalpies mean?

A

The larger the gap, the greater the covalent character of the compound and the more distorted the ions

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16
Q

Are positive lattice enthalpies those of formation or dissociation?

A

Dissociation
Energy is taken in when electrostatic attractions between ions are broken

17
Q

Are negative lattice enthalpies those of formation or dissociation?

A

Formation
Energy is released when electrostatic attractions between ions are formed

18
Q

How are theoretical lattice enthalpies calculated?

A

Using the charge and size of ions and assuming the structure is perfectly ionic

19
Q

Entropy calculation

A

Entropy change = (Sum of products entropy) - (sum of reactants entropy)

Units = Jul mol-1 K-1

20
Q

Gibbs free energy calculation

A

Gibbs free energy = enthalpy change - (temp x entropy change)

21
Q

Outline how Gibbs free energy can indicate whether or not a reaction is feasible

A

If G is less than or equal to zero = feasible
If G is more than zero = not feasible

22
Q

What causes covalent character within ionic bonds?

A
  • A small, highly positive ion and a large, highly negative ion
  • This distorts the shape of the electron cloud in the negative ion, pulling electrons towards the positive ion
23
Q

Give the equation for enthalpy of solution

A

Lattice dissociation enthalpy + enthalpy of hydration

24
Q

Define enthalpy change

A

Heat change at constant pressure

25
Q

Why is the enthalpy of hydration for Ca2+ less exothermic than Mg2+?

A
  • Ca2+ is larger
  • So it has a weaker attraction to the partially negative O- in water
26
Q

At what temp is the entropy of any element zero?

A

0K

27
Q

Explain why the enthalpy of hydration becomes less exothermic from Li+ to K+

A
  • Size of ion increases
  • So attraction between metal ion and Oδ– of water decreases
28
Q

How would you use a graph showing Gibbs free energy against temperature to calculate delta H and delta S?

A

Delta H = Intercept at y (Gibbs axis)
Delta S = Opposite sign gradient

Chemistry - Mrs McDougal (18 decks)

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