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chemistry > 17 thermodynamics > Flashcards

17 thermodynamics Flashcards

1
Q

define standard enthalpy of formation

A

enthalpy change when one mole of a compound is formed from its elements
in standard states
under standard conditions

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2
Q

define standard enthalpy of atomisation

A

enthalpy change when one mole of gaseous atoms are formed from elements in standard state
under standard conditions

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3
Q

define first electron affinity

A

enthalpy change when a mole of gaseous atoms is converted to a mole of gaseous ions
each with a single negative charge

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4
Q

define first ionisation energy

A

enthalpy change when one mole of gaseous atoms is converted to a mole of gaseous ions
each with a single positive charge

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5
Q

define lattice formation enthalpy

A

enthalpy change when one mole of solid ionic compounds is formed from its gaseous ions

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6
Q

what is mean bond enthalpy?

A

the enthalpy change when one mole of gaseous molecules
each break a covalent bond to form 2 free radicals
averaged over a range of compounds

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7
Q

what is the standard enthalpy of hydration?

A

the standard enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions

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8
Q

what is the standard enthalpy of solution?

A

the standard enthalpy change when one mole of solute dissolved to form its aqueous ions

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9
Q

what is lattice dissociation enthalpy?

A

the standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions

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10
Q

what are the two key factors that determine how exothermic a lattice enthalpy will be?

A

charge of ions
radius of ions

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11
Q

if an ion has more charge, what does this mean in terms of attraction?

A

more attraction to oppositely charged ion

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12
Q

if an ion is smaller, what does this mean in terms of attraction?

A

greater attraction to oppositely charged ion

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13
Q

what does CRAM stand for?

A

Charge
Radius
Attraction
More endo/exothermic

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14
Q

if a theoretical charge for an ionic compound is different to its actual charge, what does this mean?

A

the ionic compound has covalent character

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15
Q

what is covalent character?

A

“mimicking” covalent bond, wants to share electrons

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16
Q

what happens to the electron cloud in a compound with covalent character?

A

electron cloud becomes distorted

17
Q

what is a point charge?

A

charge in only one space

18
Q

what does the perfect ionic model say?

A

that ions are point charges and perfectly ionic

19
Q

what does the Born Haber Cycle say about ionic compounds?

A

that ions are polarisable and have covalent character

20
Q

if a compound has no covalent character, the lattice formation enthalpy calculated by the perfect ionic model is…

A

almost equal to the lattice formation enthalpy calculated by the Born Haber model

21
Q

if an ionic compound has covalent character, it’s lattice formation enthalpy calculated by the perfect ionic model will be…

A

less exothermic than the lattice formation enthalpy calculated by the Born Haber model

22
Q

how do you dissolve an ionic compound?

A
  1. break ionic bonds
  2. form bonds between water molecules and ions
23
Q

what is entropy?

A

the amount of disorder

24
Q

what is the unit of entropy?

A

JK-1 mol-1

25
Q

does an increase in disorder increase or decrease entropy?

A

increase

26
Q

does a decrease in moles decrease or increase disorder?

A

decrease

27
Q

how can you calculate ΔS?

A

sum of S products - sum of S reactants

28
Q

how do you calculate gibbs free energy?

A

ΔG = ΔH - T x ΔS

29
Q

what is ΔG and what is its units?

A

gibbs free energy
kJ mol-1

30
Q

what is ΔH and what is its units?

A

change in enthalpy
kJ mol-1

31
Q

what is T and what is its units in the gibbs free energy equation?

A

temperature
K

32
Q

what is ΔS and what is its units?

A

change in entropy
kJK-1 mol-1

33
Q

when is a reaction feaible?

A

if ΔG is less than or equal to 0

34
Q

how do you calculate the temperature at which a reaction becomes feasible?

A

T = ΔS/ΔH

chemistry (34 decks)

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