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a level chemistry > thermodynamics > Flashcards

thermodynamics Flashcards

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1
Q

in exothermic reactions are bond broken or made

A

in exothermic reactions bonds are formed

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2
Q

in endothermic reactions are bonds broken or made

A

in endothermic reactions bond are broken

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3
Q

what factor does the size of an enthalpy change depend on

A
  • the strength/energy of a bond or force

(stronger bonds /forces produce a larger enthalpy change

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4
Q

define enthalpy change of formation

A

the enthalpy change when 1 mole of substance is formed from it’s constituent elements in their standard states under standard conditions and pressure

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5
Q

write an equation for the enthalpy change of formation for NaCl

A

Na (s) + 1/2 Cl2 —-> NaCl (s)

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6
Q

define enthalpy change of lattice formation

A

the enthalpy change when one mole of an ionic compound is from from it’s component ions in a gaseous state

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7
Q

write an equation for the enthalpy change of lattice formation of NaCl

A

Na+ + Cl- —-> NaCl (s)

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8
Q

what type of energy change is enthalpy change of lattice formation and why?

A

exothermic
it is forming an electrostatic attraction (ionic bond)

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9
Q

what are the 2 factors that affect enthalpy change of lattice formation and explain why they affect it?

A

charge on ion = higher charge = strong electrostatic forces between ions = more exothermic lattice formation enthalpy

size of ion = smaller ionic radius = stronger electrostatic forces between ions = more exothermic lattice formation enthalpy

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10
Q

define enthalpy change of atomisation

A

the enthalpy change when one mole of gaseous atoms are formed

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11
Q

write the equation for the enthalpy change of atomisation of Na

A

Na (s) —> Na (g)

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12
Q

write an equation for the enthalpy change of atomisation of Cl

A

1/2 Cl2 (g) —-> Cl (g)

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13
Q

write an equation for the enthalpy change of atomisation of Br

A

1/2 Br2 (l) —-> Br (g)

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14
Q

write an equation for the enthalpy change of atomisation of S

A

1/8 S8 (s) —-> S (g)

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15
Q

what type of energy change is enthalpy change of atomisation and why

A

endothermic, as breaking bonds of attraction

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16
Q

define 1st ionisation enthalpy

A

The enthalpy change to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

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17
Q

write an equation for the 1st ionisation enthalpy for Na

A

Na (g) —-> Na+ (g) + e-

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18
Q

what type of energy change is the 1st ionisation enthalpy change

A

Endothermic, overcoming electrostatic attraction between nucleus and outer electron

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19
Q

what factors affect the 1st ionisation energy

A
  • nuclear charge
  • electron shielding
  • size of ion
20
Q

define bond dissociation enthalpy

A

the enthalpy change when 1 mole of covalent bonds are gaseous state

21
Q

write an equation for the bond dissociation enthalpy of Cl

A

Cl2 (g) —-> 2Cl (g)

22
Q

define 1st electron affinity

A

the enthalpy change to add 1 mole of electrons to 1 mole of gaseous atoms to make 1 mole of gaseous ions with a -1 charge

23
Q

write an equation for the 1st electron affinity of Cl (g)

A

Cl (g) + e- —–> Cl- (g)

24
Q

what type of energy change is 1st electron affinity

A

exothermic as an electrostatic attraction between nucleus and electron is being formed

25
Q

what factors affect 1st electron affinity

A
  • nuclear charge
  • electron shielding
  • size of atom
26
Q

define 2nd electron affinity

A

the enthalpy change when you add one mole of electrons to one mole of gaseous ions with a charge -1 to make 1 mole of gaseous ions with a -2 charge

27
Q

write an equation for the second affinity of oxygen

A

O- (g) + e- —-> O2- (g)

28
Q

what type energy change is 2nd electron affinity

A

endothermic, electron is being added to an already negatively charged ion. Repulsion between ion and electron must be overcome.

29
Q

define enthalpy of solution

A

the enthalpy change when one mole of an ionic substance is completely dissolved in water to infinite dilution

30
Q

give the equation for enthalpy of solution of MgCl2

A

MgCl2 (s) —> Mg2+ (aq) + 2Cl- (aq)

31
Q

define enthalpy of hydration

A

the enthalpy change when one mole of gaseous ions is diluted to 1 mole of aqueous ions

32
Q

give the equation for the enthalpy of hydration for Mg2+ (aq)

A

Mg2+ (aq) + (aq) —-> Mg2+ (aq)

33
Q

define lattice dissociation enthalpy

A

the enthalpy change when one mole of an ionic solid is converted to gaseous ions

34
Q

give the equation for the lattice dissociation enthalpy of MgCl2 (s)

A

MgCl2 (s) —-> Mg2+ (g) + 2Cl- (g)

35
Q

what is the equation used to calculate the value for enthalpy of solution

A

enthalpy of solution = enthalpy of lattice dissociation + enthalpy of hydration

36
Q

define enthalpy of hydration

A

forces between partial charges of delta positive and delta minus on water are attracted to ions

37
Q

is enthalpy of hydration endothermic or exothermic and why

A

exothermic as a bond is being formed

38
Q

what 2 factors affect hydration enthalpy and explain why

A

size of ion

smaller ion = higher charge density therefore stronger attraction between partial charges on water and ion
= more exothermic hydration enthalpy

charge of ion

greater charge of ion = higher charge density = stronger attraction between partial charges on water and ion = more exothermic hydration enthalpy

39
Q

define lattice dissociation enthalpy

A

electrostatic forces between postive and negative ions are overcome

40
Q

why is lattice dissociation enthalpy endothermic

A

you are breaking bonds

41
Q

what 2 factors affect the lattice dissociation enthalpy and explain why

A

size of ion

smaller ion
= higher charge density = stronger electrostatic forces between oppositely charged ions = more endothermic lattice dissociation enthalpy

greater charge on ion = higher charge density = stronger attraction between oppositely charged ions = more endothermic lattice dissociation enthalpy

42
Q

what chemical property do ionic compounds with very endothermic lattice dissociation enthalpies tend to have and why

A

ionic compounds with high lattice dissociation enthalpies tend to be insoluble as a lot of energy is needed to break the ionic lattice (electrostatic forces)

43
Q

if enthalpy of solution is exothermic then what happens to solubility when temperature increases

A

enthalpy of solution is exothermic so

solubility decreases as temperature increases

44
Q

if enthalpy of solution is endothermic then what happens to solubility as temperature increases

A

enthalpy of solution is endothermic so

solubility increases as temperature increases

45
Q
A

a level chemistry (49 decks)

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