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Principles of Chemical Engineering > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

Define Energy

A

Energy is the capacity to do work [ J ]

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2
Q

Define Work

A

Work is a form of energy which can transfer in and out of a system, stored in the organized motion of molecules [ W ]
Work is done when an object is moved against an opposing force

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3
Q

What is the Work equation

A

Work = Force * Distance
OR
dW = -Pex * dV (Pex = F/A)

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4
Q

Define Heat, Q

A

Energy of a system changed by means other than work [ J ]

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5
Q

Define a Diabatic (Diathermic) System

A

A Diabatic system is where energy is allowed in and out in the form of heat
(system in THERMAL CONTACT with surroundings)

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6
Q

Define a Adiabatic System

A

An Adiabatic System is where heat is NOT allowed in or out
(Isolated wall)

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7
Q

Wsystem > 0 means:
Work done by the system on the surr
Work done on the system by the surr

A

Work done on the system by the surr

system is SELFISH likes to GAIN W&Q

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8
Q

Qsystem > 0 means:
Heat transferred from system to surr
Heat transferred on the system by the surr

A

Heat transferred on the system by the surr

system is SELFISH likes to GAIN W&Q

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9
Q

Define Internal energy

A
  • The total energy of the system
  • It is a STATE FUNCTION: depends on current state
  • It is an EXTENSIVE PROPERTY: depends on amount of matter
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10
Q

There must be a change in _______ for a change in internal energy

A

There must be a change in TEMPERATURE for a change in internal energy

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11
Q

What is the First Law of Thermodynamics
(Internal energy equation)

A

ΔU = Q + W
(heat to system & work done on system)

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12
Q

ΔU equation

A

ΔU = Ufinal - Uinitial

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13
Q

2) Isobaric Process effect on ΔU = Q + W

A

Pressure is constant

ΔU = Q + W

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14
Q

Isochoric Process effect on ΔU = Q+ W

A

Volume is constant
No area under curve for P/V graph, no U

ΔU = Q

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15
Q

Adiabatic Process effect on ΔU = Q + W

A

No transfer of heat in the system, ΔQ = 0

ΔU = Wad

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16
Q

Isothermal Process effect on ΔU = Q + W

A

Temperature is constant, ΔT = 0 ∴ ΔU

Q = -W

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17
Q

Cyclic Process (e.g. engines) effect on ΔU = Q + W

A

Same initial and final stages, ΔU = 0

Q = -W

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18
Q

Define a Reversible process

A

A Reversible process is never more than INFINITESIMALLY FAR from EQUILIBRIUM and an infinitesimal change in EXTERNAL conditions can REVERSE the process.

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19
Q

What are Reversible Expansion conditions

A

net F = Fgas - Fex = 0

Pex = P,
Pex (external pressure)

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20
Q

Define a Irreversible process

A

A Irreversible process CANNOT be reversed by a INFINITESIMAL change in EXTERNAL conditions

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21
Q

What is the Ideal gas equation

A

PV = nRT

22
Q

What is the Non-ideal gas equation

A

PV = ZnRT

Z is the compressibility factor / Van Waals eq.

23
Q

What is an indicator diagram

A

P/V graph to calculate expansion work

24
Q

How to study changes in energy due to heat

A
  • Calorimetry studies
  • Heat capacities and enthalpies
25
Q

Define Heat capacity

A

Heat capacity is the heat required to raise the temperature of the system by one kelvin

26
Q

What does the slope of U/T graph give

A

The HEAT CAPACTIY of the system at that TEMPERATURE

27
Q

A change in internal energy can be identified with the ____ supplied at a constant volume

A

A change in internal energy can be identified with the HEAT supplied at a constant volume

Qv = CvΔT

28
Q

Define Enthalpy

A

Enthalpy is the internal energy req. to CREATE a system (U) & amount of energy req. to MAKE ROOM for it (PV)

Is a STATE FUNCTION => INDEP. OF PATH

29
Q

(What is the Cp and Cv relationship)

A

Cp - Cv = nR

30
Q

What changes occur when gas expands adiabatically

*****SLIDE 9 L3

A

1) T= const, V increases U const

2) T reduces, V= const.

31
Q

What is the perfect gas law

A

PiVi / PfVf = Ti / Tf

32
Q

Define Standard enthalpy change

A

Is the change in enthalpy for a process in stnd states

33
Q

Define Standard state

A

Standard state is 298K and 1bar

34
Q

Define Standard enthalpy of transition

A

Standard enthalpy of transition is the enthalpy change accompanying a PHASE CHANGE in stnd states

35
Q

Define Standard reaction enthalpy

A

Is the change in enthalpy when reactants change to products in stnd states

36
Q

Define Hess’ Law

A

The standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions

37
Q

Define Exact Differentials

A

Exact Differentials are systems taken along a path (STATE FUNCTION)

38
Q

Define Inexact Differential

A

When a system is heated, total energy transferred as heat is sum of individual contributions along each point of the path
(PATH FUCTION, DEP. ON PATH)

39
Q

Define Standard enthalpy of formation

A

Change in enthalpy for formation of compound from its CONSTITUENT ELEMENTS in their reference states.

40
Q

Define Spontaneous changes

A

Spontaneous changes are accompanied by dispersal of energy into a more disordered form

41
Q

Define Non-spontaneous changes

A

Non-spontaneous changes require something ‘SPECIAL’ to happen

42
Q

Define the Second Law of Thermodynamics

A

No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work

43
Q

What does increasing Entropy do
(2nd Law of ThermoD.)

A

Increasing Entropy increases DISORDER and RANDOMIZED MOTION

44
Q

What does negative value of entropy mean

A

Becomes less disorders, energy must be provided, NON SPONTANEOUS

45
Q

How to prove Entropy as a State Function

A

1) dQrev/Trev = 0 true for CARNOT CYCLE
2) “ true for ANY SUBSTANCE
3) “ true for ANY CYCLE

46
Q

What is the Carnot Cycle ***

A

1) Reversible isothermal expansion (Th)
2) Reversible adiabatic expansion (Th -> Tc)
3) Reversible isothermal compression (Tc)
4) Reversible adiabatic compression (Tc -> Th)

Look up picture L6 S14

47
Q

True of any cycle L6 S20??

A

huh??

48
Q

What are the states in decreasing disorder

A

Gases > Liquids > Solids

49
Q

Define the Third Law of Thermodynamics

A

As T approaches 0, the absolute entropy tends towards zero
No spatial disorder
No thermal motion

50
Q

What are Third Law Entropies

A

Entropies reported on the basis that S(0) = 0,
S°(T)

Principles of Chemical Engineering (3 decks)

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