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chemistry A-level 2 > Thermodynamic > Flashcards

Thermodynamic Flashcards

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1
Q

what is enthalpy change

A

heat change at constant pressure

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2
Q

what reaction is the first ionisation energy

A

endothermic

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3
Q

first electron affinity

A

energy change when 1 mole of gaseous atoms gain an electron to form 1 mole of gaseous 1- ions

N (g) + e- -> N-(g)

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4
Q

what reaction is the first electron affinity

A

exothermic

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5
Q

second electron affinity

A

energy change when 1 mole of gaseous 1- ions gain an electron to form 1 mole of gaseous 2- ions

V- (g) + e- -> V2- (g)

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6
Q

what reaction is the second electron affinity

A

endothermic

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7
Q

enthalpy of atomisation

A

enthalpy change when 1 mole of gaseous atoms are formed from an element in its standard state

Na(s) -> Na(g)
1/2 F2(g) -> F (g)

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8
Q

what reaction is the enthalpy of atomisation

A

endothermic

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9
Q

lattice enthalpy

A

enthalpy change when 1 mole of an ionic compound is formed from its constituent gaseous ions

Na+(g) + CL-(g) -> NaCl (s)
Zn2+(g) + 2Br-(g) -> ZnBr2

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10
Q

what reaction is the lattice enthalpy

A

exothermic

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11
Q

lattice dissociation enthalpy

A

enthalpy change when 1 mole of an ionic compound is broken into its constituent gaseous ions

NaCl(s) -> Na+(g) + Cl-(g)

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12
Q

what reaction is the lattice disassociation enthalpy

A

endothermic

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13
Q

bond dissociation enthalpy

A

enthalpy change when 1 mole of covalent bonds is broken in the gaseous state

Cl2 (g) -> 2Cl (g)

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14
Q

what reaction is the bond dissociation enthalpy

A

endothermic

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15
Q

what does the perfect ionic model assume:

A
  • bonding is 100% ionic
  • ions exist as perfectly spherical point charges
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16
Q

what does the value for lattice enthalpy on the born-haber cycle not match

A

the perfect ionic model

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17
Q

perfect ionic model
Al2O3

A

Al3+ is a highly charged small ion that is able to distort the electron density of the O2- ion toward itself

Al2O3 has a degree of covalent character

18
Q

how to cause a greater covalent character

A
  • a highly charged small cation
  • a large negatively charged anion
19
Q

what does the difference between born haber cycle and the perfect ionic model mean

A

if they differ significantly, there is a larger degree of covalent character

20
Q

to increase electrostatic attraction:

A
  • higher the charge of +ve and -ve
  • the smaller the ionic radii
21
Q

enthalpy of solution

A

enthalpy change when 1 mole of an ionic compound is dissolved in water

22
Q

what reaction is the enthalpy of solution

A

can be endothermic or exothermic

23
Q

enthalpy of hydration

A

enthalpy change when 1 mole of gaseous ions are dissolved in water

24
Q

what reaction is the enthalpy of hydration

A

exothermic

25
Q

what is entropy (s)

A

measure of disorder within a system or substance
JK-1mol-1

26
Q

what is the entropy at 0 kelvins

A

entropy is also 0

27
Q

order of entropy

A

solid - lowest
liquid
gas - highest

28
Q

what features does a high entropy have

A
  • large Mr/ molecules
  • higher temperature
  • liquid -> gas causes an increase
29
Q

how to work out the change in entropy

A

change in entropy of products - change in entropy of reactants

30
Q

what is Gibbs energy

A

gives us a way of linking enthalpy and entropy changes during a reaction. tells us about the feasibility of a reaction

31
Q

gibbs energy formula

A

change in Gibbs = change in enthalpy - kelvin x entropy change

G = H - TS

convert entropy into kJmol-1

32
Q

how can a reaction to be feasible

A

change in gibbs must be equal to or less than 0

33
Q

formula to see when a reaction is feasible

A

T = change in enthalpy / change in entropy

34
Q

change in entropy - +ve
change in enthalpy - -ve

A

-ve = feasible

35
Q

change in entropy -ve
change in enthalpy +ve

A

+ve = not feasible

36
Q

change in entropy -ve
change in enthalpy -ve

A

only feasible at low temperatures

37
Q

change in entropy +ve
change in enthalpy +ve

A

only feasible at high temperatures

38
Q

why does water melt

A

melts at 0 degrees/ 273k . this is because the value of delta G for the change is 0

39
Q

what is a spontaneous reaction

A

has sufficiently low activation energy to take place immediately
+ve entropy value

40
Q

what is a feasible reaction

A

has a high activation energy, so must be supplied for the reaction to start

41
Q

when does covalent character occur

A

covalent character occurs in ions when two joined ions have different sizes/charged meaning the distribution of the charge in not even

42
Q

how to work out lattice enthalpy

A

LE = hyd - sol

chemistry A-level 2 (6 decks)

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