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SEM2 > Chem Midterm #1 > Flashcards

Chem Midterm #1 Flashcards

1
Q

In what direction does heat flow from objects?

A

High to low
- measure of particle’s average kinetic energy
- objects at same T do not exchange heat energy

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1
Q

What is the first law of thermodynamics?

A

U=q+w (internal energy= heat + work)
- conservation of energy
- energy is transferred, but remains constant

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2
Q

Are breaking bonds exothermic or endothermic?

A

endothermic (heat absorbed)
- amount of heat depends on system size

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3
Q

Are forming bonds exothermic or endothermic?

A

exothermic (heat released)
- all combustion reactions

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4
Q

What is enthalpy (H)?

A
  • measure in difference of heat content
  • between final and initial states
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5
Q

What is heat capacity?

A

Amount of heat required to raise temperature of a substance by 1 C/K
(C=q/T) in JK-1

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6
Q

What is molar heat capacity vs specific heat?

A

Molar (Cm or C)- raise 1 mole through 1C or K (JK-1mol)
Specific (Cs)- raise 1 gram through 1C or K (Jg-1K-1)

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7
Q

What is advantageous of using a bomb calorimeter instead of a coffee-cup calorimeter?

A
  • higher temperatures (that would melt the coffee cup)
  • more accurate (measures temp. and pressure)
  • at high pressure
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8
Q

What is work?

A
  • the energy exchange that results when a force moves
    an object through a distance
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9
Q

What is compression (and how does it affect work)?

A
  • work is done on the system by the surroundings
    (positive work)
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10
Q

What is expansion (and how does it affect work)?

A
  • work is done by the system on the surroundings
    (negative work)
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11
Q

When does work=0?

A

when the change in volume is 0, as systems cannot expand/compress

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11
Q

When does U=0?

A

when there is no change in temperature, as KE is related to temp.

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12
Q

What does the naught symbol refer to?

A

standard
- temp. must be specified (as it is not part of the definition of a standard state)

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13
Q

What do thermochemical equations describe? (rule 1)

A

the energy changes associated with
1 mole of something.

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14
Q

What happens to H if we reverse the reaction?

A

Its sign is also reversed

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15
Q

Is thermochemistry associated with how?

A

No, only interested in energy differences between initial and final states (we can add thermochemistry equations to produce other equations)

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16
Q

What is enthalpy of fusion?

A
  • when we fuse one mole of something
  • ex: 1 mole solid -> liquid
  • always positive
  • temperature remains constant
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17
Q

What is enthalpy of vaporization?

A
  • enthalpy change when we vapourize 1 mole of liquid to gas
  • always positive
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18
Q

What is enthalpy of sublimation?

A
  • when we sublime 1 mole solid -> 1 mole gas
  • always positive
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19
Q

What is enthalpy of combustion?

A
  • when we burn 1 mole of something completely in O2
  • always negative (energy released)
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19
Q

What is enthalpy of atomization?

A
  • associated with the formation of 1 mole of ATOMS from its elements
  • always positive (bonds broken)
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20
Q

What is the Standard Molar Enthalpy of Formation?

A
  • enthalpy change when we form one mole of a substance
    from its elements in their standard states at 1 bar
  • always 0 in its most stable state
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20
Q

What is Hess’ law?

A
  • overall process is the sum of H naught for the individual steps of the process
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21
Q

Which two elements are liquid in their most stable form?

A

Hg (mercury)
Br (bromine

22
Q

Which two elements on the right side of the periodic table are solid in their most stable forms?

A

P4 (phosphorus)
S8 (sulphur)

23
Q

Noble gases in their most stable form

A

ex: He (g)

24
Q

What is bond enthalpy?

A
  • energy required to break a mole of covalent bonds in the gas phase (does
    not hold for liquids or solids)
  • always positive
  • measure of a covalent bond’s strength
  • come from average values
  • for gases only
24
Q

What is lattice energy?

A

change in energy
that occurs when an ionic solid is separated into isolated ions in the gas phase

25
Q

What is the born-haber cycle?

A
  • going step by step to find final enthalpy (sublimation, IE, bond enthalpy, etc)
26
Q

What is the magnitude of lattice energies dependent on?

A
  • charge of ions and their separation
  • coulomb’s law
27
Q

What does occuring spontaneous mean?

A

the reaction will occur, as
written, on its own with no external intervention
- molecules have freedom of motion

28
Q

What is entropy?

A
  • measure of how dispersed the energy of a
    system is among the different possible ways that system can contain energy
  • dependent on system size
29
Q

Positional vs thermal entropy

A

positional- distribution of species in space
thermal- distribution of energy among species

30
Q

What is the second law of thermodynamics?

A

in any spon. process, total entropy of universe must increase
S>0: spontaneous
S=0: equilibrium
S<0: non-spon

31
Q

What is the third law of thermodynamics?

A

a perfect crystalline substance is at absolute 0 (T=0K, S=0)

32
Q

When does Sm (standard molar entropy) increase?

A
  • melting and vaporization
  • solid or liquid is dissolved in a solvent
  • increasing mass
  • increasing number of atoms in the molecule
    -increasing molecular freedom or flexibility
33
Q

When does Sm (standard molar entropy) decrease?

A
  • gas is dissolved in a solvent
  • for gases: decreases with increasing pressure
34
Q

When is a system at equilibirum?

A

at melting and boiling points

35
Q

What is entropy/enthalpy driven?

A

entropy driven: H=0
enthalpy driven: S=0

36
Q

When is reaction spontaneous in regards to enthalpy and entropy?

A

∆HRxn is negative and ∆SRxn is positive

37
Q

When is reaction non- spontaneous in regards to enthalpy and entropy?

A

If ∆HRxn is positive and ∆SRxn is negative

38
Q

What does Gibbs Free Energy help us with?

A

when H and S are both positive/negative; to decide if a reaction is spontaneous or not

39
Q

∆Grxn is NEGATIVE

A

spontaneous

40
Q

∆Grxn is ZERO

A

equilibirum

41
Q

∆Grxn is POSITIVE

A

non-spontaneous

42
Q

Spontaneity if +S,+H

A

Reaction spontaneous
at HIGH enough T, i.e.,
when T∆S > ∆H (entropy driven)

43
Q

Spontaneity if +S,-H

A

Reaction ALWAYS
spontaneous (as written),
as ∆G < 0

44
Q

Spontaneity if -S,+H

A

Reaction NEVER
spontaneous (as written),
as ∆G > 0

45
Q

Spontaneity if -S,-H

A

Reaction spontaneous
at LOW enough T, i.e.,
when T∆S < ∆H

46
Q

What is ∆G°f?

A

∆G for the reaction in which 1 mole of a substance in its
standard state is formed from its elements in their standard states

47
Q

What is ∆G°m,f?

A

measure of stability with respect to decomposition of a compound into
its elements under standard conditions

48
Q

What if ∆G°m,f is negative?”

A

the elements that make up
the compound form the compound spontaneously (compound is more stable than the elements/products favoured)

49
Q

What if ∆G°m,f is positive?

A

the compound decomposes
spontaneously into its elements (compound is less stable than the elements/reactants favoured)

50
Q

Q=K

A

equilibrium

51
Q

Q>K

A

right to left (ln(Q/K) is positive, non-spon)

52
Q

Q<K

A

left to right (ln(Q/K) is negative, spon)

53
Q

∆Grxn is…

A

quantitative expression of distance from equilibrium

54
Q

K >1

A

ln K is positive and ∆G° is negative

55
Q

K <1

A

ln K is negative and ∆G° is positive

56
Q

What are state functions?

A

internal energy and enthalpy

SEM2 (4 decks)

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