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AQA; A-level Chemistry > 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 standard states under standard conditions - 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 standard states under standard conditions - exothermic

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3
Q

enthalpy of neutralisation

A

enthalpy change when 1 mole of water is formed in a reaction between an acid and an alkali under standard conditions - exothermic

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4
Q

ionisation enthalpy

A

first: enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions
second: enthalpy change when each ion in one mole of gaseous 1+ ions loses one electron to form one mole of gaseous 2+ ions
-endothermic

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5
Q

electron affinity

A

First: enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions
- exothermic
Second: enthalpy change when each ion in one mole of gaseous 1- ions gains one electron to form one mole of gaseous 2- ions
-endothermic

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6
Q

enthalpy of atomisation

A

enthalpy change when one mole of gaseous atoms is produced from an element in its standard state - endothermic

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7
Q

hydration enthalpy

A

enthalpy when one mole of gaseous ions become hydrated (dissolved in water) - exothermic

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8
Q

enthalpy of solution

A

enthalpy change when one mole of an ionic solid is dissolved - varies

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9
Q

bond dissociation enthalpy

A

enthalpy change when one mole of covalent bonds is broken in the gaseous state - endothermic

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10
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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11
Q

lattice enthalpy of dissociation

A

enthalpy change when one mole of a solid ionic compound is broken into its constituent ions in the gas phase - endothermic

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12
Q

enthalpy of vaporisation

A

enthalpy change when one mole of a liquid is turned into a gas - endothermic

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13
Q

enthalpy of fusion

A

enthalpy change when one mole of a solid is turned into a liquid - endothermic

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14
Q

born-haber cycle

A

ionise metal –> down 2nd ea –> down
1st ea non-metal —> up
up
atomise non-metal lattice
up of
atomise metal formation
up
start line: elements in standard states
down (enthalpy formation)
base line: solid ionic compound <———————————-

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15
Q

enthalpy change definition

A

change in heat content at constant pressure

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16
Q

Hess’s law?

A

The enthalpy change for a reaction is independent of the route taken
A —> B = A—>C—>B

17
Q

enthalpy of formation hess law

A

elements enthalpy of formation always 0
arrows pointing up from constituent elements
sum of product enthalpy - sum of reactant enthalpy

18
Q

enthalpy of combustion hess law

A

arrows pointing down to oxides
reaction across top often enthalpy of formation

19
Q

bond enthalpy hess law

A

arrows pointing down to gas atoms
bond enthalpies are mean not specific for compound so not very accurate

20
Q

equation for enthalpy change and conversion to kJ/mol
(calorimetry)

A

q = mcAt
q: heat energy given out (J)
m: mass of substance heated (g)
AT: temperature rise (K)
c: specific heat capacity (J/g/K)
Then
/1000 for kJ
Finally
enthalpy change/mol = q/number of moles reacting

21
Q

problems with calorimetry calculations + solution

A

heat loss major problem - to reduce you can measure heat capacity of calorimeter as a whole

22
Q

enthalpy of solution hess cycle

A

gas ions —-> ionic solid (lattice enthalpy formation)
gas ions —-> dissolved (aq) ions (hydration enthalpy)

arrows pointing down from gas ions to

ionic solid ——-> dissolved (aq) ions (enthalpy of solution)

23
Q

trend in lattice enthalpy in regards to ionic bonding

A

greater magnitude of lattice enthalpy, greater ionic bonding and vice versa
compounds with smaller ion and/or greater charge have stronger attraction so greater lattice enthalpy

24
Q

how to find experimental lattice enthalpy?

A

born-haber cycle

25
Q

what is perfect ionic model?

A

theoretical calculation for lattice enthalpy that considers size, charge and arrangement of ions in lattice - assumes structure is perfectly ionic

26
Q

problem with perfect ionic model

A

often distortion of ions in ionic compound (not perfectly spherical) - they have covalent character
bigger difference between theoretical and real value in general, the greater the covalent character
still ionic bonding but some covalent properties such as low solubility, lower melting point/conductivity than expected

27
Q

entropy

A

Entropy (S) is how disordered something is and is measured in J/mol/K
Gases have most entropy
Entropy will naturally increase over time

28
Q

entropy

A

Entropy (S) is how disordered something is and is measured in J/mol/K
Gases have most entropy
Entropy will naturally increase over time

29
Q

how does entropy vary with temperature?

A

Zero at absolute zero and increases with temperature
Big increases in entropy at state changes - greatest from liquid to gas as entropy substantially larger in gases than solids or liquids

30
Q

entropy change

A

change in S = [sum S products] - [sum S reactants]
reactions with increase in entropy are favourable
sometimes very small change so unable to tell if it will be positive or negative

31
Q

Gibbs free energy change

A

change in G combines change in H and change in S
AG (kJ/mol) = AH (kJ/mol) - T (K) AS (J/mol/K)
need to convert AS to kJ/mol/K
Feasible reaction if AG less than or equal to 0
Depends on temperature if feasible or not
AG = 0 is the point at which reaction becomes feasible
If feasible still may not occur due to having very high activation energy

AQA; A-level Chemistry (9 decks)

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