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IB Chemistry > 5+15 energetics > Flashcards

5+15 energetics Flashcards

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
Hess' law states that the enthalpy change of a chemical reaction is ________ whether the change is brought about in __________ or ______________
the same, one stage, many intermediate stages
26
what is bond enthalpy?
the **amount of energy** needed to **break one mole of bonds** in a **gaseous molecule** under standard conditions
27
how can you calculate ∆H from bond enthalpy?
∆HBE (rxts) - ∆HBE (pdts)
28
why is the theoretical ∆H value (from calculations with bond enthalpies) different from the experimental ∆H value
bond enthalpies do not take into account intermolecular forces
29
the oxygen-containing molecule that absorbs short-wavelength UV radiation is...
ozone
30
why is ozone important?
- it absorbs harmful UV radiation - harmful UV radiation would damage cells in plants and animals
31
radiation of a [shorter/longer] wavelength is required to break the bond in oxygen than breaking the bonds in ozone
shorter
32
why is shorter wavelength required for the O-O bonds oxygen to be broken (when compared w ozone)?
- 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
33
how does ozone shield the earth from UV (use eqns)
-
34
what are the equations/steps in the photodissociation of ozone that protect the earth from harmful radiation?
-
35
what are CFCs used for? (short, 4)
1. aerosols 2. refrigerants 3. solvents 4. plastics
36
what is the chemical formula of CFCs
CCl2F2
37
what are the three steps involved in the destruction of the ozone layer by CFC?
1. initiation 2. propagation 3. termination
38
write out the equations for the destruction of the ozone layer by CFC
-
39
why can one Cl* destroy many ozone molecules?
Cl* is re-generated and can continue to destroy the ozone molecules
40
what are the equations for the reactions of nitrogen oxides with ozone?
-
41
lattice energy is used for _______ (type) compounds
ionic
42
what is lattice energy/∆Hºlattice
it is the standard enthalpy change when one mole of a **(s) ionic compound** is separated into **(g) ions** under standard conditions
43
lattice energy is [endo/exothermic]
endothermic
44
what relationship explains how lattice energy depends on the charges and sizes of ions?
|lattice energy|∝| q+r-/r+ + r- |
45
what is the standard enthalpy change of atomisation/∆Hºat?
it is the standard enthalpy change when one mole of **(g) atoms** is formed **from the element** in its standard states
46
how do you find the ∆Hºat of diatomic molecules
∆Hºat = 1/2∆HBE
47
what is 1st electron affinity, ∆HEA
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
the process of 1st ∆HEA is [exo/endothermic]
exothermic
49
why is the process of 1st ∆HEA exothermic?
energy released due to the **attraction** formed btw the gaseous atom and electron
50
what is 2nd electron affinity, ∆HEA
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
does the 2nd electron affinity release energy or absorb energy?
absorbs energy
52
why is the 2nd electron affinity endothermic?
energy is absorbed to overcome the repulsion between the singly negatively charged ion and the e-
53
what is 1st ionisation energy/∆HIE
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
for all ∆HIE, the process is...
endothermic
55
why is there an increase in successive ionisation energy?
- 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
what is the standard enthalpy change of hydration/ ∆Hºhyd?
it is the standard enthalpy change when **one mole of (g) ions** forms **one mole of hydrated ions** in **water** under standard conditions
57
what affects hydration energy?
size and charge of ions
58
why is hydration exothermic?
energy is released due to the formation of ion-dipole interactions btw ions and polar water molecules
59
what is the equation for the relationship of hyd energy w size and charge of the ions?
|q+/r+| or |q-/r-|
60
what is the standard enthalpy change of solution/∆Hºsoln?
it is the standard enthalpy change where 1 mole of a **solute** is dissolved in a **solvent** to **infinite dilution** under standard conditions
61
what is the equation for ∆Hºsoln?
∆Hºsoln = ∆Hºlattice + ∆Hºhyd
62
why is ∆Hºsoln exothermic? (ref to bonds)
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
why is ∆Hºsoln endoothermic? (ref to bonds)
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
why is there a difference in theoretical and experimental lattice energy?
- 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
what are the mnemonics for calculations of ∆H?
CR – Clash Royale FP – Face Palm BR – Be Real SP – Singapore Poly GP – General Paper
66
what is the mnemonic for the Born-Haber cycle?
F – formation A – atomisation I – ionisation L – lattice energy
67
how does the ∆Hºhyd change down grp 17?
becomes less exothermic
68
why does the ∆Hºhyd become less exothermic down grp 17?
- ionic radius increases - as hyd energy ∝ |q-/r-| - thus, less exothermic
69
why is the compound less likely to be soluble if ∆Hºhyd > 0?
- 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
what is entropy?
the degree of disorder or randomness in a system
71
what is the unit for entropy?
J mol-1 K-1
72
what is the formula for change in entropy/∆Sº?
Sºpdt - Sºrxt
73
what affects entropy of a system? (4)
1. change in the no. of particles (esp g) 2. change in temp 3. change in phase 4. mixing of particles
74
what leads to incr entropy?
- incr in no. of particles - incr in temp - phase change to gas - mixing of particles
75
an increase in temperature causes entropy to [incr/decr]
incr
76
why does an incr in temperature an incr in entropy?
- 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
draw a Boltzmann energy distribution curve to show the effect of temperature on energy of the particles
-
78
how does the change in the number of particles affect entropy? why?
- more gaseous molecules -> system is more disorderly - thus entropy incr
79
why is there an incr in entropy when a solid substance melts?
- 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
why does a change in phase to a gas lead to a large incr in entropy?
- 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
how does the mixing of particles lead to an increase in entropy for a gas?
- mixing leads to a higher state of disorder - more ways of arranging the particles - thus incr entropy
82
in mixing liquids, why does entropy incr?
- mixing leads to incr in total vol - more ways to distribute the particles and distribute their energy
83
entropy in dissolution of solid ionic cmpd
84
when ∆S>0 and ∆H>0, when is the reaction spontaneous? why?
- 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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