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CHEM 203 > PPT 2 > Flashcards

PPT 2 Flashcards

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1
Q

What is the approximate energy of molecular rotrations?

A

0.01 kJ/mol

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1
Q

What is the approximate energy of molecular vibrations?

A

10 kJ/mol

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2
Q

What is the approximate energy of molecular excitations?

A

1000 kJ/mol

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3
Q

When is energy easily redistributed?

A

when more energy can be absorbed without much change in temerature

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4
Q

When is energy not easily redistributed?

A

when more energy is needed to reach a hiogher state, higher change in temperature required

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5
Q

What does diathermic mean?

A

allows energy to leave the system as heat

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6
Q

What is an example of diathermic?

A

our skin or biological membranes

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7
Q

What is adiabatic?

A

does not allow energy to leave system as heat

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8
Q

What is a system with no walls called?

A

an open system

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9
Q

What is a system with diathermic walls called?

A

a closed system

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10
Q

What is a system with adiabatic walls called?

A

an isolated system

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11
Q

What is the state function that corresponds to the energy inside a system?

A

internal energy

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12
Q

What is internal energy?

A

sum of all contributions of energy of all atoms, ions, molefcules that are present in the system

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13
Q

What are the different possible types of energy in a system?

A

translational
rotational
vibrational
electronic
nuclear
intermolecular

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14
Q

Is internal energy and intensive or extensive property?

A

extensive

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15
Q

Why are vibrational and electronic energy disregarded when calculting specific heat capacity?

A

at room temperature, most molecules will stay in their lowest energy state (population of N2 is negligible compared to N1)

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16
Q

Why is translational energy all populated?

A

N2/N1 = 1, equal amounts at all energy states, continuous, have same number of molecules in them within those translational modes

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17
Q

Why can we calculated delta E when there is an excitation?

A

energy is quantized

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18
Q

Is the change in internal energy a state function (does the path matter)?

A

yes, path does not matter

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19
Q

Why does delta U = 0 under isothermal expansion?

A

when T is constant, KE remains unchanged = no intermolecular attractions between molecules, so PE remains unchanged even when the volume changes

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20
Q

Which type of energy has an unchanged volume and no other forms of work are done?

A

internal energy

21
Q

Why is qv a state function but q is not?

A

we have defined the path, whatever heat is being lost/gained, it is only under constant volume conditions

22
Q

When can internal energy be calculated?

A

when the container has rigid walls

23
Q

What is the relation between U and T?

A

a straight line

24
Q

How to measure the heat capacity of U vs. T graph at constant volume?

A

the slope

25
Q

What is the first law of internal energy?

A

internal energy of an isolated system is constant

26
Q

What are the values of w and q for an isolated system?

A

w = 0, since it is isolated, it cannot expand
q = 0, since it is isolated, there is no exchange in heat (adiabatic)

27
Q

Why is delta U = 0 for an isolated system?

A

energy is conserved

28
Q

What is the equipartition of energy theroem?

A

the energy of a molecule is equally divided among all types of motions or degrees of freedom

29
Q

When does the equipartition theory apply?

A

when kT&raquo_space; delta E

30
Q

How much energy does each translation d.f. possess?

A

1/2 kT

31
Q

How much energy does each rotational d.f. possess?

A

1/2 kT

32
Q

How much energy does each vibrational d.f. possess?

A

1 kT

33
Q

When are vibrational modes important?

A

at high temperature, at low temperatures it rarely satisfies kT&raquo_space; delta E

34
Q

How many d.f. does a single atom have? How are they distributed?

A

3 - all translational

35
Q

How many d.f. does a linear molecule have? How are they distributed?

A

depends on the molecule
ex: diatomic = 6
3 translational
2 rotational
3N - 5 (1) vibrational

36
Q

How many d.f. does a nonlinear molecule have? How are they distributed?

A

depends on the molecule
ex: triatomic = 6
3 translational
3 rotational
3N - 6 (3) vibrational

37
Q

How are d.f. measured for a molecule with N atoms?

A

3N

38
Q

When are calculated energy levels most similar to the measured ones?

A

for monoatomic gases

39
Q

Why is there a discrepency between calculated and measured energy levels are there are more molecules?

A

vibrational modes are taken into account

40
Q

Is enthalpy an intensive or extensive property?

A

extensive

41
Q

what conditions do enthalpy occur under?

A

isobaric - constant pressure

42
Q

Is enthalpy a state function? Does the path matter?

A

yes, path does not matter

43
Q

What is the change in enthalpy?

A

equal to the energy transferred to or from the system as heat, under constant pressure

44
Q

What is an endothermic reaction?

A

increase in enthalpy of a system under constant pressure

45
Q

What is an exothermic reaction?

A

decrease in enthalpy of a system under constant pressure

46
Q

What is the relationship between enthalpy and temperature?

A

propoortional

47
Q

Is molar enthalpy an intensive or extensive property?

A

intensive

48
Q

What is the difference between Cp,m and Cv,m?

A

R

49
Q

Why is Cp,m always greater than Cv,m?

A

for Cp,m expansion can occur (lost) but for Cv,m not work can be done since the change in volume = 0

When a system is free to expand, some of the energy supplied as heat is free to escape back into the suroundings as work. Therefore, the rise in temperature at constant pressure is not as great as at constant volume and the heat capacity is corresponding,y greater.

50
Q

When do I use R and when do I use Kb?

A

R - units are J/mol
Kb - units are J

51
Q

What is the standard state of a substance?

A

the pure substance at 1 barr

CHEM 203 (4 decks)

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