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Thermodynamics > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What is a pure substance?

A

A pure substance is one that is uniform in chemical composition.

A mixture of various chemical elements or compounds can also qualify as a pure substance if it is homogeneous.

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2
Q

Can a mixture of oil and water be classified as a pure substance?

A

No, because oil is not soluble in water, forming two chemically dissimilar regions.

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3
Q

What are the three major phases of a pure substance?

A
  • Solid
  • Liquid
  • Gas
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4
Q

How do temperature and pressure affect the phases of a pure substance?

A

Heating and compression can lead to phase changes.

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5
Q

What happens when heat is added to a fixed mass of water at constant pressure?

A

The temperature increases, and the specific volume also increases until boiling starts, then the temperature remains constant.

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6
Q

What is the saturated region in the context of heating water?

A

A region where the temperature remains constant, but the specific volume increases.

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7
Q

What is the critical point?

A

The point at which the saturated liquid and saturated vapour states are identical.

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8
Q

What occurs at pressures above the critical pressure?

A

There is no notable phase change; only one phase exists.

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9
Q

What is the vapor pressure?

A

The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phase at a given temperature.

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10
Q

What does the equilibrium vapor pressure indicate?

A

It indicates the evaporation rate of a liquid.

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11
Q

What is the Antoine equation used for?

A

To compute the vapor pressure of most elements.

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12
Q

What are the three forms of energy in a thermodynamic system?

A
  • Potential energy
  • Kinetic energy
  • Internal energy
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13
Q

What is internal energy (U)?

A

The sum of all microscopic forms of energy, including internal kinetic and potential energies.

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14
Q

What is enthalpy (H)?

A

The sum of internal energy and the product of pressure and volume (U + PV).

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15
Q

What are specific heat capacities?

A

Properties defined at constant volume (Cv) and constant pressure (Cp).

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16
Q

What is a common reference state for water in thermodynamics?

A

The state of saturated liquid at 0.01°C is taken as the reference state.

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17
Q

True or False: The values of u, h, and s can be measured directly.

A

False, they are calculated from measurable properties.

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18
Q

What happens to the specific volume of water when heated at high pressures?

A

The specific volume of the saturated liquid is larger, and the specific volume of the saturated vapor is smaller.

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19
Q

What is the significance of the triple point in phase diagrams?

A

It is the state where all three phases of a pure substance coexist in equilibrium.

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20
Q

Fill in the blank: The ________ is the temperature at which the vapor pressure equals the ambient atmospheric pressure.

A

[normal boiling point]

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21
Q

What happens when pressure is applied to water vapor?

A

The volume of the water vapor decreases with increasing pressure until it reaches saturation.

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22
Q

What does the term ‘superheated region’ refer to?

A

The gas is at a temperature higher than that needed to start boiling for a specified pressure.

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23
Q

What is the relationship between internal energy and temperature?

A

At higher temperatures, molecules possess higher kinetic energies, resulting in higher internal energy.

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24
Q

What are the SI units for internal energy (U)?

A

J or kJ

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25
What is the specific internal energy (u)?
Internal energy per unit mass, with units of J/kg or kJ/kg.
26
What is the significance of the Antione constants?
They are specific to a substance and used in the Antoine equation to calculate vapor pressure.
27
What is an extensive property in thermodynamics?
A property that depends on the amount of substance, such as internal energy (U), enthalpy (H), and entropy (S).
28
What is the general trend of specific heat capacities for ideal gases?
Cp is always higher than Cv.
29
What is the relationship between specific heat capacities for diatomic and monoatomic gases?
* Diatomic gases: γ ≈ 1.4 * Monoatomic gases: γ ≈ 1.667
30
What is the reference state for internal energy and entropy in thermodynamics?
°C is taken as the reference state, and the internal energy and entropy are assigned zero values at that state.
31
What reference state is used for refrigerant-134a?
The state of saturated liquid at -40°C is taken as the reference state, with enthalpy and entropy assigned zero values.
32
What may cause different values for properties at the same state in thermodynamic tables?
Different reference states may lead to different values for some properties.
33
What is the importance of the reference state in thermodynamic calculations?
The reference state chosen is of no consequence in calculations as long as values from a single consistent set of tables or charts are used.
34
What are some sources of thermodynamic data?
* Thermodynamic tables (e.g., steam table, air table) * Thermodynamic charts (e.g., Mollier diagram, psychometric charts) * Computer software (e.g., Chemsep, ASPEN properties, Multiflash)
35
What is an equation of state (EOS)?
An equation that relates the pressure, temperature, and specific volume of a substance.
36
What is the most common equation of state for gases?
The ideal-gas equation.
37
What assumptions does the ideal gas model make?
* The gas consists of very small particles. * Collisions among particles are perfectly elastic. * Interactions among molecules are negligible except during collisions.
38
Under what conditions does the ideal gas model deviate?
At high pressures and low temperatures.
39
What are the equations of state for real gases?
* The use of the compressibility factor * The virial equations * Cubic equations of state
40
What does the compressibility factor (Z) correct for?
Deviations from the ideal gas behavior.
41
What is the principle of corresponding states?
The Z factor for all gases is approximately the same at the same reduced pressure and temperature.
42
What is the virial equation used for?
To represent the P-v-T behavior of a substance accurately over a wider range.
43
What are the virial coefficients?
Coefficients in the virial equation that can be determined experimentally or theoretically from statistical mechanics.
44
What is the acentric factor?
A parameter used to characterize fluids, obtained from the plot of P vs. T.
45
What is the first cubic equation of state?
The van der Waals equation.
46
What are the two main constants in the van der Waals equation?
* a (attraction term) * b (repulsion term)
47
What does the van der Waals equation account for?
Intermolecular forces and the volume occupied by gas molecules.
48
What are the two most useful cubic equations of state?
* Peng-Robinson * Soave-Redlich-Kwong
49
What is a steam table?
A set of thermodynamic data for liquid water or steam at different conditions (temperature and pressure).
50
What regions are categorized in a steam table?
* Compressed liquid * Saturated * Superheated
51
What is the quality of steam?
The fraction of vapor in the liquid-vapor mixture.
52
What is the purpose of the superheated steam table?
To provide data for specific internal energy, enthalpy, and specific volume of superheated steam.
53
What is the significance of interpolation in superheated steam data?
To estimate values between known data points for accurate thermodynamic calculations.
54
What is the typical behavior of compressed liquid properties with respect to pressure?
Variation of properties of compressed liquid with pressure is very mild ## Footnote Increasing the pressure 100 times often causes properties to change less than 1 percent.
55
What is a general approximation for compressed liquid in the absence of specific data?
Treat compressed liquid as saturated liquid at the given temperature.
56
What are the desired properties of a refrigerant?
* A boiling point that is somewhat below the target temperature * A high heat of vaporization * A moderate density in liquid form * A relatively high density in gaseous form * High critical temperature * Non-corrosive * Low toxicity and flammability * Low environmental impact
57
What is refrigerant 134a also known as?
1,1,1,2-Tetrafluoroethane.
58
Which table contains data on compressed liquid properties?
Table A–7.
59
List some examples of substances that have compressed liquid data available in the text.
* Air * Nitrogen (N2) * Oxygen (O2) * Carbon monoxide (CO) * Carbon dioxide (CO2)
60
What is the approach used to calculate the enthalpy change for carbon dioxide from 25°C to 100°C?
Constant heat capacity approach.
61
What are ideal gas tables used for?
To provide data on internal energy (u), enthalpy (h), and entropy (s) for ideal gases.
62
True or False: Compressed liquid tables are commonly available.
False.
63
What is the significance of the NIST chemistry work book in thermodynamics?
It is a source of thermodynamic data.
64
Which software is mentioned as a source of thermodynamic data?
Aspen properties.
65
Fill in the blank: A refrigerant is a working fluid used in the refrigeration cycle of air conditioning systems and heat pumps where it undergoes a repeated phase transition from a liquid to a gas and back again, known as _______.
phase transition.
66
What is the main reason for the lack of compressed liquid data?
The relative independence of compressed liquid properties from pressure.
67
What type of refrigerant is liquid ammonia classified as?
A refrigerant.
68
What table contains both saturated and superheated data for refrigerant 134a?
Table A-11.
69
What is the function of the DECHEMA database?
It is a source of thermodynamic data.
70
What is the function of the International Association for the Properties of Water and Steam?
It provides thermodynamic data.

Thermodynamics (2 decks)

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