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3rd Year Fall > C2301 Midterm 2 > Flashcards

C2301 Midterm 2 Flashcards

1
Q

What are the levels of energy separations in quantum mechanics?

A

Etrans>Erot>Evib>Eelec

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2
Q

What is the relative probability of finding a molecule in a corresponding energy state called?

A

The Boltzmann Distribution

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3
Q

What are Degrees of Freedom?

A

The number of variables needed to describe the motion of a particle completely.

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4
Q

Degrees of Freedom for Translational Motion

A

3 (x,y,z)

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5
Q

Degrees of Freedom for Rotational Motion

A

Linear: 2
Nonlinear: 3

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6
Q

Degrees of Freedom for Vibrational Motion:

A

Linear: 3N-5
Nonlinear: 3N-6

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7
Q

Define heat

A

The amount of E that flows across a boundary of 2 objects due to a temperature difference.

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8
Q

What is the spontaneous direction of flow for heat?

A

High T - Low T

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9
Q

What are the 3 ways heat is transferred?

A
  1. Convection
  2. Conduction
  3. Radiation
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10
Q

Transitory Property

A

Only appears during a change of state of system; not related to initial and final states. Path function. Ex) Heat

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11
Q

Heat capcity

A

the measure of E needed to change the temperature of a substance a given amount.
Dependent on material and temperature.

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12
Q

Extensive quantity

A

Depends on amount and nature of material

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13
Q

Heat capacity at constant pressure (eqn)

A

Cp=dqp/dT

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14
Q

Heat capacity at constant volume (eqn)

A

Cv=dqv/dT

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15
Q

Shomate equation (Explanation)

A

Describes the heat capacity of a material as a function of temperature, where the coefficients were determined from curve fitting.

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16
Q

How are Cp,m and Cv,m related for gases? (eqn)

A

Cp,m=Cv,m+R

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17
Q

Why is Cp>Cv for gases?

A

In a constant pressure process, gas expands as its T increases, and the system does work on the surroundings. As a consequence, not all of the heat flow into the system can be used to increase dU. In constant volume, no work occurs; thus, all heat is used to increase dU.

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18
Q
A
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18
Q

How are Cp and Cv related for liquids and solids?

A

Cp is approximately equal to Cv.

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19
Q

Why are Cp and Cv approximately equal for liquids and solids?

A

Any volume change upon heating is negligible.

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20
Q

What quantity represents heat at constant volume?

A

delta U

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21
Q

What quantity represents heat at constant pressure?

A

delta H

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22
Q

What is a fundamental relation in defining the other relations, which connects internal energy change, volume, pressure, and heat?

A

dU=d_q-pdV
where d_q is an inexact differential

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23
Q

Define enthalpy

A

Enthalpy is measured as the heat transfer by the system for a process occuring at constant pressure.

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24
Q

How can Cv,m be used to find heat?

A

qv=nCv,mdT
where d represents delta T

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25
Q

How can Cp,m be used to find heat?

A

qp=nCp,mdT
where d represents delta T

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26
Q

What assumptions are made when relating Cv and Cp to other quantities in a cycle?

A

We assume no chemical reactions or phase changes occur.
Also assume Cv and Cp are constant over the temperature change occuring.

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27
Q

What can we say about isobaric processes?

A

w=-PextdV
where dV=Vf-Vi

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28
Q

What can we say about isochoric processes?

A

w=0 and dU=q

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29
Q

What can we say about isothermal processes?

A

dT=0 and dU=dH=0

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30
Q

What can we say about adiabatic processes?

A

q=0 and dU=w

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31
Q

What can we say about the internal energy in a closed cycle

A

dUcycle=0

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32
Q

Relations for reversible adiabatic systems

A

PiVi^y=PfVf^y
(Tf/Ti)=(Vf/Vi)^1-y
where y=Cp/Cv

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33
Q

How can we set up the equations for an irreversible adiabatic system?

A

dU=w
nCv,mdT=-Pext(Vf-Vi)
Can carry the above forward to solve for Tf in terms of Pf, Pi, Pext, and Cv,m.

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34
Q

What does reversible adiabatic compression lead to in terms of T?

A

Heating

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35
Q

What does reversible adiabatic expansion lead to in terms of T?

A

Cooling

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36
Q

Thermochemistry

A

Concerned with heat flow into or out of a reaction system

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37
Q

Endothermic

A

A reaction where E is absorbed by the system

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38
Q

Exothermic

A

A reaction where E is released by the system.

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39
Q

What is the E stored in chemical bonds referred to as?

A

Potential E

40
Q

What is typical standard state?

A

1 bar, 25C (298.15K)

41
Q

Standard enthalpy of formation

A

enthalpy change of a rxn in which only 1 mol of the species of interest, with only pure elements in their most stable states under standard conditions appear as reactants.

42
Q

Hess’s Law

A

the enthalpy change for any sequence of chemical rxns that sum to the overall rxn is the same as that of the base rxn.

43
Q

What parameters are held constant in O2 bomb calorimetry?

A

Volume

44
Q

What reaction happens in O2 bomb calorimetry?

A

Combustion

45
Q

How is the calorimetry constant, Ccal, determined?

A

A standard (usually benzoic acid) of known molar enthalpy of combustion can be obtained to accurately determine the heat capacity constant of the bomb calorimeter.

46
Q

How can internal energy be calculated in oxygen bomb calorimetry?

A

dU=ms/MsdUc+mH2O/Mh20CpdT+CcaldT=0

47
Q

What is another name for constant pressure calorimetry?

A

Coffee-cup calorimetry

48
Q

What assumptions can be made for solids and liquids when used in constant pressure (or volume) calorimetry?

A

dH is approximately equal to dU

49
Q

List the names of all phase transitions of matter.

A

Can refer to pg 14 of unit 3 notes.

50
Q

Start of unit 4 notes

A
51
Q

What are the two main state functions and path functions in unit 4?

A

State: U and H
Path: q and w

52
Q

What is the result if we multiply the following partial differentials together: dP/dT x dV/dT x dT/dP

A

-1

53
Q

What is the name of the coefficient denoted alpha?

A

Isobaric volumetric thermal expansion coefficient

54
Q

What symbol denotes the isothermal compressibility?

A

Kappa sub T

55
Q

What is the differential equation that relates the change in U with T and V?

A

dU=(dU/dT)dT+(dU/dV)dV
where italics represent partials

56
Q

What is the internal pressure relation?

A

dU/dV=T(dP/dT)-P

57
Q

What is the internal P of an ideal gas?

A

0

58
Q

What was the Joule experiment?

A

Attempted to measure dU/dV for an ideal gas.

59
Q

Describe the experimental apparatus of the Joule experiment.

A

Consider it has two interacting systems in a rigid adiabatic enclosure. The 2 systems are 1) water bath and 2) volume within left and right glass bulbs. These together are isolated.
Look further into this experiment

60
Q

What was the Joule-Thomson Experiment?

A

Seeked to measure dH/dV and is far more accurate than the previous experiment.

61
Q

Explain the Joule-Thomson experiment and apparatus.

A

Gas flows from a high-pressure cylinder into a low-pressure cylinder. Gas is forced through a porous plug in which the piston moves to maintain a constant pressure, until all of the gas has been transferred through the plug.

62
Q

What is the result of the Joule-Thomson experiment?

A

After transfer of gas, there is a large pressure drop across the plug and the temperature change of the gases can be measured. This is an adiabatic process.

63
Q

What remains constant for the process in the Joule-Thomson experiment?

A

Enthalpy; isoenthalpic.

64
Q

Joule-Thomson coefficient

A

limiting ratio of dT and dP; experimentally determined; denoted u_J-T

65
Q

What dominates when u_J-T is positive?

A

Attraction

66
Q

What dominates when u_J-T is negative?

A

Repulsion

67
Q

What happens when P is decreased for positive Joule-Thomson coefficients?

A

Gas is cooled

68
Q

What happens when P is decreased for negative Joule-Thomson coefficients?

A

Gas is heated

69
Q

Inversion Temperature

A

u_J-T=0

70
Q

When can dH be determined by measuring qp? (3)

A
  1. Any arbitrary process at constant P
  2. In a closed system
  3. Where only P-V work is carried
71
Q

Heat capacity at constant P (differential definition)

A

Cp=dH/dT

72
Q

If Cp is constant, dHp can be represented by this simplified formula:

A

dHp=nCp,mdT

73
Q

What is the approximation for enthalpy of solids and liquids (assuming they are a function of T alone)?

A

dH=n integral,Ti-Tf(Cp,mdT)

74
Q

What are the 2 statements/formulations of the second law?

A
  1. It is impossible for a system to undergo a cyclic process that turns all heat completely into work done on the surroundings.
  2. It is impossible for a process to occur that has the sole effect of removing a quantity of heat from an object at lower T and transferring it to an object at higher T.
75
Q

Classical definition of entropy

A

Entropy is the amount of E not available to do work

76
Q

Definition of entropy (differential eqn form)

A

dS=dqrev/T

77
Q

What is the spontaneous heat flow according to entropy?

A

Higher q to lower q (dq<0)

78
Q

What is the following sentence termed?
For any process that proceeds in an isolated system, there is a unique direction of spontaneous change and dS>0 for the spontaneous process.

A

The 2nd Law of Thermodynamics

79
Q

Is S positive or negative for expansion?

A

+

80
Q

Is S positive or negative for compression?

A

-

81
Q

Is entropy a path or state function?

A

State

82
Q

What is the entropy for phase changes?

A

dvapS=dvapH/Tvap

83
Q

What is the statistical definition of entropy?

A

Entropy is a measure of the degree to which E is dispersed into the available E levels associated with random molecular motion of all molecules in a system

84
Q

What is a single particle microstate?

A

Any particular E state of a single molecules, i.e. its quantized unit, which is combined translational, rotational, and vibrational E states

85
Q

N-particle microstate

A

Any quantized state of a whole system of molecules.
Consists of the single particle microstates of all molecules.

86
Q

What are the 5 rules for the number of N-particle microstates?

A
  1. At any given instant in time, the total E is dispersed throughout one N-particle microstate.
  2. In the next instant, Etot is in a different N-p.m. of equal energy.
  3. Each accessible equal E N-p.m. is equally possible for the system
  4. The number of single particle microstates for a single molecule is large, and for N-particle microstates is enormus.
  5. Under a given set of conditions, the number of accessible N-p.m. is the number of ways its thermal E can be dispersed among the trans, rot, and vib E levels of all its molecules
87
Q

What is the Ludwig Boltzmann eqn?

A

S=kBln(omega)

88
Q

If entropy is positive, did the system transition from smaller N-p.m. (initial) to larger N-p.m. (final) or the reverse case?

A

Smaller-larger

89
Q

What conclusions were made based on the statistical entropy approach to the spontaneous isothermal expansion of a gas?

A

dEn is inversely proportional to the square of the length of a 1D box.

90
Q

How can entropy be calculated in an isothermal process?

A

dSsys=nRln(Vf/Vi)

91
Q

How can the entropy change in the surroundings be found?

A

dSsurr=dqsurr/T= -dqsys/T

92
Q

What condition is required so that the entropy of a system can decrease in a spontaneous process?

A

dStotal>0

93
Q

Why is entropy often called Time’s arrow?

A

For an isolated system, entropy can only increase, not decrease; i.e. spontaneous systems lead to an increase of Stotal.

94
Q

3rd Law of Thermodynamics

A

The entropy of a pure, perfectly crystalline substance is zero at 0K

95
Q

How many microstates are in a perfectly crystalline solid?

A

1

96
Q

What is residual entropy?

A

The entropy at 0K for not perfectly ordered crystals

97
Q

What is the order of magnitude of entropy among the phases of matter?

A

solid<liquid<gas

98
Q
A

3rd Year Fall (5 decks)

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