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IB Chemistry > 5+15 energetics > Flashcards

5+15 energetics Flashcards

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1
Q

what is enthalpy?

A

measure of the heat energy contained in a substance

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2
Q

enthalpy is also ________

A

potential energy

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3
Q

the triangle means…

A

change

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4
Q

bond breaking requires energy to be _________ and bond forming requires energy to be _______

A

absorbed, released

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5
Q

the higher the enthalpy of a substance, the _____ stable it is

A

less

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6
Q

exothermic reactions result in a increase in the temperature of the _______________

A

surrounding

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7
Q

are the products or reactants more energetically stable in exothermic reactions?

A

products

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8
Q

draw an enthalpy diagram for an exothermic reaction

A

-

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9
Q

reactants of endothermic reactions are _____ energetically stable than that of the products

A

more

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10
Q

the first law of thermodynamics is: energy may be exchanged btw the ______ and the _________ but the total energy is ________

A

system, surroundings, constant

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11
Q

what are the standard conditions?

A

100kPa
1 moldm-3
298K

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12
Q

what is standard state?

A

the most pure, stable state of a substance measured at 100kPa (and 298K)

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13
Q

what is the enthalpy change of formation, ∆Hºf? (defin.)

A

enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions of 298K and 100kPa

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14
Q

what is the enthalpy change of formation is 0 for…

A

elements

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15
Q

how do you use ∆Hºf to find ∆Hºreaction

A

∆Hºpdts - ∆Hºrxts

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16
Q

what is the definition of standard enthalpy change of combustion, ∆Hºc?

A

enthalpy change when one mole of substance in its standard state is completely burned in excess oxygen under standard conditions

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17
Q

∆Hºc is always -ve/+ve

A

-ve

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18
Q

what is the standard enthalpy change of neutralisation? ∆Hºneu

A

enthalpy change when one mole of water is formed between the neutralisation of an acid and a base under standard conditions

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19
Q

why do weak acids and bases have less exothermic enthalpy change as compared to strong acids and bases?

A
  • WA+B only slightly ionised
  • part of the heat evolved from neutralisation is used to dissociate WA/B
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20
Q

what is the equation used to calculate the amount of heat transferred out of a substance?

A

Q = mc∆T

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21
Q

what are the units for Q=mc∆T

A

Q – J
m – g
c – J g^-1K^-1
∆T – K/Cº

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22
Q

in an exothermic reaction, how can ∆H be found with Q?

A

-Q/nlim

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23
Q

in an endothermic reaction, how can ∆H be found with Q?

A

+Qnlim

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24
Q

what is the specific heat capacity of water?

A

4.18 Jg^-1K^-1

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25
Q

Hess’ law states that the enthalpy change of a chemical reaction is ________ whether the change is brought about in __________ or ______________

A

the same, one stage, many intermediate stages

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26
Q

what is bond enthalpy?

A

the amount of energy needed to break one mole of bonds in a gaseous molecule under standard conditions

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27
Q

how can you calculate ∆H from bond enthalpy?

A

∆HBE (rxts) - ∆HBE (pdts)

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28
Q

why is the theoretical ∆H value (from calculations with bond enthalpies) different from the experimental ∆H value

A

bond enthalpies do not take into account intermolecular forces

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29
Q

the oxygen-containing molecule that absorbs short-wavelength UV radiation is…

A

ozone

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30
Q

why is ozone important?

A
  • it absorbs harmful UV radiation
  • harmful UV radiation would damage cells in plants and animals
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31
Q

radiation of a [shorter/longer] wavelength is required to break the bond in oxygen than breaking the bonds in ozone

A

shorter

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32
Q

why is shorter wavelength required for the O-O bonds oxygen to be broken (when compared w ozone)?

A
  • O2 has double bond
  • thus bond order =2
  • O3 has resonance -> partial double bond character
  • thus bond order =1.5
  • less energy required to break weaker bond
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33
Q

how does ozone shield the earth from UV (use eqns)

A

-

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34
Q

what are the equations/steps in the photodissociation of ozone that protect the earth from harmful radiation?

A

-

35
Q

what are CFCs used for? (short, 4)

A
  1. aerosols
  2. refrigerants
  3. solvents
  4. plastics
36
Q

what is the chemical formula of CFCs

A

CCl2F2

37
Q

what are the three steps involved in the destruction of the ozone layer by CFC?

A
  1. initiation
  2. propagation
  3. termination
38
Q

write out the equations for the destruction of the ozone layer by CFC

A

-

39
Q

why can one Cl* destroy many ozone molecules?

A

Cl* is re-generated and can continue to destroy the ozone molecules

40
Q

what are the equations for the reactions of nitrogen oxides with ozone?

A

-

41
Q

lattice energy is used for _______ (type) compounds

A

ionic

42
Q

what is lattice energy/∆Hºlattice

A

it is the standard enthalpy change when one mole of a (s) ionic compound is separated into (g) ions under standard conditions

43
Q

lattice energy is [endo/exothermic]

A

endothermic

44
Q

what relationship explains how lattice energy depends on the charges and sizes of ions?

A

|lattice energy|∝| q+r-/r+ + r- |

45
Q

what is the standard enthalpy change of atomisation/∆Hºat?

A

it is the standard enthalpy change when one mole of (g) atoms is formed from the element in its standard states

46
Q

how do you find the ∆Hºat of diatomic molecules

A

∆Hºat = 1/2∆HBE

47
Q

what is 1st electron affinity, ∆HEA

A

1st electron affinity is the standard enthalpy change when one mole of (g) electrons is added to one mole of (g) atoms to form one mole of singly charged gaseous ion

48
Q

the process of 1st ∆HEA is [exo/endothermic]

A

exothermic

49
Q

why is the process of 1st ∆HEA exothermic?

A

energy released due to the attraction formed btw the gaseous atom and electron

50
Q

what is 2nd electron affinity, ∆HEA

A

2nd electron affinity is the standard enthalpy change when one mole of (g) electrons is added to one mole of singly negatively charged (g) ion to form one mole of doubly charged (g) ion

51
Q

does the 2nd electron affinity release energy or absorb energy?

A

absorbs energy

52
Q

why is the 2nd electron affinity endothermic?

A

energy is absorbed to overcome the repulsion between the singly negatively charged ion and the e-

53
Q

what is 1st ionisation energy/∆HIE

A

the minimum energy required to remove one mole of electrons from one mole of (g) atoms to form one mole of singly positively charged (g) ion

54
Q

for all ∆HIE, the process is…

A

endothermic

55
Q

why is there an increase in successive ionisation energy?

A
  • incr amt of energy req to remove successive e- from incr-ly +ve ion
  • incr electrostatic FOA btw +vely charged nucleus and -ve valence e-
56
Q

what is the standard enthalpy change of hydration/ ∆Hºhyd?

A

it is the standard enthalpy change when one mole of (g) ions forms one mole of hydrated ions in water under standard conditions

57
Q

what affects hydration energy?

A

size and charge of ions

58
Q

why is hydration exothermic?

A

energy is released due to the formation of ion-dipole interactions btw ions and polar water molecules

59
Q

what is the equation for the relationship of hyd energy w size and charge of the ions?

A

|q+/r+| or |q-/r-|

60
Q

what is the standard enthalpy change of solution/∆Hºsoln?

A

it is the standard enthalpy change where 1 mole of a solute is dissolved in a solvent to infinite dilution under standard conditions

61
Q

what is the equation for ∆Hºsoln?

A

∆Hºsoln = ∆Hºlattice + ∆Hºhyd

62
Q

why is ∆Hºsoln exothermic? (ref to bonds)

A

energy released from hydration of ions is more than energy used to break up the solid lattice structure and in H-bonding btw water molecules

63
Q

why is ∆Hºsoln endoothermic? (ref to bonds)

A

energy released from hydration of ions is less than energy used to break up the solid lattice structure and in H-bonding btw water molecules

64
Q

why is there a difference in theoretical and experimental lattice energy?

A
  • partial covalent character in the ionic bond is not accounted for in theoretical values
  • this is due to polarisation of anion by cation of high charge density
65
Q

what are the mnemonics for calculations of ∆H?

A

CR – Clash Royale
FP – Face Palm
BR – Be Real
SP – Singapore Poly
GP – General Paper

66
Q

what is the mnemonic for the Born-Haber cycle?

A

F – formation
A – atomisation
I – ionisation
L – lattice energy

67
Q

how does the ∆Hºhyd change down grp 17?

A

becomes less exothermic

68
Q

why does the ∆Hºhyd become less exothermic down grp 17?

A
  • ionic radius increases
  • as hyd energy ∝ |q-/r-|
  • thus, less exothermic
69
Q

why is the compound less likely to be soluble if ∆Hºhyd > 0?

A
  • it is endothermic
  • meaning energy released from hydration is not enough to compensate for the lattice energy required to break down the crystal lattice structure
70
Q

what is entropy?

A

the degree of disorder or randomness in a system

71
Q

what is the unit for entropy?

A

J mol-1 K-1

72
Q

what is the formula for change in entropy/∆Sº?

A

Sºpdt - Sºrxt

73
Q

what affects entropy of a system? (4)

A
  1. change in the no. of particles (esp g)
  2. change in temp
  3. change in phase
  4. mixing of particles
74
Q

what leads to incr entropy?

A
  • incr in no. of particles
  • incr in temp
  • phase change to gas
  • mixing of particles
75
Q

an increase in temperature causes entropy to [incr/decr]

A

incr

76
Q

why does an incr in temperature an incr in entropy?

A
  • particles move more randomly + vigorously
  • amt of energy in system incr
  • broadening of the Boltzmann energy distribution (more particles possess more energy)
    • more ways of distributing energy in the system + greater disorder
77
Q

draw a Boltzmann energy distribution curve to show the effect of temperature on energy of the particles

A

-

78
Q

how does the change in the number of particles affect entropy? why?

A
  • more gaseous molecules -> system is more disorderly
  • thus entropy incr
79
Q

why is there an incr in entropy when a solid substance melts?

A
  • in a solid atoms are vibrate in an orderly arrangement in fixed positions
  • when solid changes to liquid the atoms slide over each other in a disorderly arrangement
  • incr in disorder -> incr in entropy
80
Q

why does a change in phase to a gas lead to a large incr in entropy?

A
  • atoms in gaseous state are free to move about
  • widely spaced -> large incr in volume
  • thus there are more ways to arrange the atoms + distribute energy btw particles
81
Q

how does the mixing of particles lead to an increase in entropy for a gas?

A
  • mixing leads to a higher state of disorder
  • more ways of arranging the particles
  • thus incr entropy
82
Q

in mixing liquids, why does entropy incr?

A
  • mixing leads to incr in total vol
  • more ways to distribute the particles and distribute their energy
83
Q

entropy in dissolution of solid ionic cmpd

A
84
Q

when ∆S>0 and ∆H>0, when is the reaction spontaneous? why?

A
  • when temp is high
  • as incr temp results in T∆S becoming more positive
  • ∆G = ∆H - T∆S
  • hence ∆G becomes more negative

IB Chemistry (12 decks)

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