Deck 10: Transport of Energy and Matter

Question 1

What distinguishes passive diffusion from other types of diffusion?

A)Passive diffusion transports only certain molecular species from a region of high to a region of low concentration.
B)Passive diffusion always transports material from a region of high to a region of low concentration.
C)Passive diffusion requires special processes and structures within the membrane to be present.
D)Passive diffusion requires a threshold concentration gradient to be present, before it can take place.

Answer 1

Passive diffusion always transports material from a region of high to a region of low concentration.

Question 2

In Arrhenius's formula, on which one of these factors does the factor D₀ depend at the molecular scale?

A)speed of particles
B)temperature
C)the frequency with which the particle attempts to overcome the activation energy barrier
D)distance between particles

Answer 2

the frequency with which the particle attempts to overcome the activation energy barrier

Question 3

The temperature of Earth's interior is 3000°C. Taking the surface temperature as 0°C, what is the temperature at the bottom of a mine shaft 2 km deep?

A)10°C
B)50°C
C)60°C
D)120°C

Answer 3

60°C

Question 4

Which of the following characteristics does NOT apply to thermal conductivity?

A)depends on the conducting material
B)depends on temperature
C)is higher for metals than for liquids
D)depends on the mass of the material

Question 5

Which of these characteristics does NOT apply to the rate of heat flow?

A)depends on the material
B)proportional to the temperature gradient
C)inversely proportional to the square of the length over which heat flows
D)proportional to the cross-sectional area

Question 6

The parameter set for the diffusion of carbon in silicon contains the pair of points (ln(D), 1/T) with values (-30.16, 6.0 × 10^-4) and (-37.07, 8.0 × 10^-4). What is the value of D₀ in m²/s?

A)8.03 × 10^-4 m²/s
B)3.72 × 10^-5 m²/s
C)8.03 × 10^-5 m²/s
D)3.72 × 10^-10 m²/s

Question 7

The diffusion constant for Cu in Si, at temperature 1394°C is larger than that of Ge in Si by a factor of 3.58 × 10⁶. If, after a certain time, Ge diffuses an average distance of 1 ìm, how far on average does Cu diffuse during the same time interval?

A)3.58 m
B)3.78 mm
C)1.89 mm
D)1.89 ìm

Question 8

Which of the following is NOT a transport phenomenon?

A)heat conduction
B)conversion of oxygen to carbon dioxide
C)diffusion of oxygen between capillaries and lungs
D)viscosity

Question 9

If the activation energy of a certain molecule is 3.0 eV, by what factor does the diffusion constant increase when the temperature changes from 30°C to 37°C?

A)6.7
B)10.1
C)13.4
D)391.0

Question 10

Which of these statements best describes how thermal relaxation time depends on the geometric characteristics of a body?

A)It is proportional to the volume.
B)It is proportional to the linear dimension.
C)It is proportional to the square of the linear dimension.
D)It is proportional to the square root of the volume.

Question 11

What is the metabolic rate (expressed in kJ/day) required by a person of surface area 1.5 m² and wearing clothing (with the thermal conductivity of felt) of thickness = 1 cm, to maintain a body temperature of 37°C, when the air temperature is 0°C?

A)19180 kJ/day
B)9590 kJ/day
C)1918 kJ/day
D)222 kJ/day

Question 12

What thickness of clothing (assume it to have the conductivity of felt) must a human wear in order to experience the same total rate of heat loss as an animal with the same body temperature and 10% of the surface area, and having a layer of fat under its skin 1.50 cm thick?

A)9.00 cm
B)2.50 cm
C)0.40 cm
D)0.25 cm

Question 13

How does doubling the width of a membrane affect the time it takes for a particle to pass through the membrane?

A)Time is doubled.
B)Time is four times longer.
C)Time is longer by a factor of .
D)Time remains the same.

Question 14

What distinguishes interstitial diffusion from substitutional diffusion?

A)Interstitial diffusion occurs only when the diffusing atom and the atoms in the lattice are the same.
B)Interstitial diffusion does not have to displace other atoms, which requires more activation energy and so substitutional diffusion is generally less probable.
C)Interstitial diffusion occurs more slowly than substitutional diffusion.
D)Interstitial diffusion requires a high enough temperature before it can take place.

Question 15

What is the dominant mechanism of cooling the skin when exposed to air at temperature 27°C?

A)radiation
B)convection
C)conduction
D)perspiration

Question 16

If two materials are in contact, with the first material having twice the thermal conductivity of the second, what can be deduced about the temperature gradients in the two materials near the interface between them?

A)They are the same.
B)They depend on factors other than thermal conductivities.
C)The temperature gradient of the second is half that of the first.
D)The temperature gradient of the second is twice that of the first.

Question 17

The parameter set for the diffusion of oxygen in silicon contains the pair of points (ln(D), 1/T) with values (-28.42, 6.0 × 10^-4) and (-34.54, 8.0 × 10^-4). What is the activation energy in eV?

A)5.28 eV
B)2.64 eV
C)2.04 eV
D)1.31 eV

Question 18

Which one of the following statements correctly describes a semipermeable membrane?

A)It blocks interactions across the membrane.
B)It allows transfers across the membrane in both directions.
C)It blocks some system components but not others.
D)It does not allow the conduction of heat.

Question 19

The rate of cooling of an object is proportional to the difference in temperature between the body and its surroundings. How much faster will a cup of water at boiling point (100.0°C) cool outside where the temperature is -10.0°C compared to in a room at temperature 20°C?

A)0.4 times
B)0.5 times
C)0.7 times
D)1.4 times

Question 20

For a given time period, how does diffusion length depend on temperature?

A)decreases with temperature
B)independent of temperature
C)increases with temperature
D)can both increase and decrease with temperature

Question 21

Einstein's diffusion formula may be applied to the transport of potassium ions across membranes of nerve cells.

Question 22

The diffusion coefficient of one fluid in another medium depends on both the fluid and the medium.

Question 23

For diffusion of a molecule through a membrane, the activation energy can, in general, be estimated as accurately as the pre-factor D₀.

Question 24

When calculating the heat loss from the human body, the metabolic rate can be higher than this heat loss.

Question 25

In order to have life, biological systems have to exist away from equilibrium.

Question 26

Fick's law is similar to Fourier's law, except that mass instead of energy is being transported.

Question 27

Discuss how you might measure the diffusion coefficient of one substance in another.

Question 28

The history of life on Earth demonstrates that it existed long before the age of the Sun or Earth as calculated by Lord Kelvin. Discuss how this dilemma was resolved in more recent times.

Question 29

The diffusion coefficient increases with activation energy of an atom moving through a matrix of other particles.

Question 30

The "R-value" is stamped onto insulating material to indicate the "thermal resistivity" of the material, and is proportional to the inverse of the thermal conductivity coefficient k. The units of R are (foot²)(°F)(British thermal unit/hour)^-1(inch^-1). Find the equation that relates R-values to thermal conductivity when the latter is expressed in SI units (Wm^-1K^-1).

Question 31

Heat conduction may, in practice, be implemented as a reversible process.

Question 32

In Fick's law, as stated in Eqs. [10.2] and [10.3], the assumption was made that all particles were travelling perpendicular to the plane defining the membrane. How would you generalize this result, considering the particles move randomly in all directions?

Question 33

Calculate the heat flux (heat flow per unit area) from the body of a person (surface area = 1.5 m²) wearing clothing of thickness = 1 cm, when the clothing is (i) pure cloth, and (ii) cloth, with 50% air space, when the outside temperature is -20°C and body temperature is 37°C. Use values of ë from Table 10.1. What effect does moisture caused by perspiration have when entering the air spaces?

Question 34

For a given volume, how would the shape of an animal determine the rate of heat loss through its skin?

Question 35

When taking a deeper breath than usual, the alveoli expand to a make a larger surface area; however, each breath takes longer. Discuss how this will affect oxygen intake by the lungs.

Question 36

The metabolic rate depends only on the ambient temperature.

Question 37

The distance that a particle diffuses is proportional to the duration of time.

Question 38

Using the procedure in Example 10.1, derive a general formula for the cooling time of a planetary body of given internal and surface temperatures and a rocky crust of thickness = l. How would this cooling time be affected if the crust gradually formed, so that it was thinner in the past and thickened as the planet cooled down?

Question 39

Briefly discuss why passive diffusion is inadequate as a mechanism for transporting ions and molecules through a membrane.

Question 40

Discuss in general terms what factors affect the rate of uptake of oxygen by mammals of different sizes, considering that the heartbeat rate determines the speed at which blood circulates from oxygen uptake by the lungs to its return to the lungs for replenishment.