Thermodynamics Quiz 9-15, 1-8

A process during which the temperature remains constant is called a(n) _____ process.

A process during which the temperature remains constant is called an isothermal process.

At _____ point the saturated liquid and the saturated vapor states are identical.

At critical point the saturated liquid and the saturated vapor states are identical.

A steady-flow system involves changes with time anywhere within the system or at the system boundaries.

False, a steady-flow system involves no changes with time anywhere within the system or at the system boundaries.

A vapor that is about to condense is superheated vapor; otherwise it is saturated vapor.

False, a vapor that is about to condense is saturated vapor; otherwise it is superheated vapor.

In electric heaters, electrical energy is converted to potential energy.

False, in electric heaters, electrical energy is converted to sensible internal energy.

Mechanical energy is the form of energy that can be converted to mechanical work indirectly by a mechanical device such as a propeller.

False, mechanical energy is the form of energy that can be converted to mechanical work completely and directly by a mechanical device such as a propeller.

The macroscopic forms of energy are those related to the molecular structure of a system and the degree of the molecular activity, and they are independent of outside reference frames.

False, the macroscopic forms of energy are those a system possesses as a whole with respect to some outside reference frame.

Which of the following statements is true?

It is possible to create entropy, but it is not possible to destroy it.

On a P-v diagram, what does the area under the process curve represent?

It represents the boundary work for quasi-equilibrium process.

Which of the following physical quantities are conserved during a process? (Check all that apply.)

Mass, energy, and momentum are conserved during a process.

Is it possible to develop a reversible heat-engine cycle that is more efficient than a Carnot cycle operating between the same temperature limits?

No, it would violate the Carnot principle.

Is it possible to develop an actual heat-engine cycle that is more efficient than a Carnot cycle operating between the same temperature limits?

No, it would violate the Carnot principle.

Consider two solid blocks, one hot and the other cold, brought into contact in an adiabatic container. After a while, thermal equilibrium is established in the container as a result of heat transfer. The first law requires that the amount of energy lost by the hot solid be equal to the amount of energy gained by the cold one. Does the second law require that the decrease in entropy of the hot solid be equal to the increase in entropy of the cold one?

No, the second law does not require the decrease in entropy of the hot solid to be equal to the increase in entropy of the cold one.

An experimentalist claims to have raised the temperature of a small amount of water to 150°C by transferring heat from high-pressure steam at 120°C. Is this a reasonable claim?

No, this is not a reasonable claim. Heat cannot flow from a low-temperature medium to a higher temperature medium.

The entropy of a hot baked potato decreases as it cools. Is this a violation of the increase of entropy principle?

No, this is not a violation of the increase of entropy principle because the entropy of the surrounding air increases even more during the given process, making the total entropy change positive.

_____ is the ratio of the mass of vapor to the total mass of the mixture.

Quality is the ratio of the mass of vapor to the total mass of the mixture.

During a heat transfer process, the entropy change of incompressible substances, such as liquid water, can be determined from ΔS = mcavgln(T2/T1). Identify the correct relation for thermal energy reservoirs, such as large lakes.

The correct relation for thermal energy reservoirs, such as large lakes is ΔS = Q/T1

A fixed mass of an ideal gas is heated from 50 to 80°C at a constant volume of (a) 1 m3 and (b) 3 m3. For which case do you think the energy required will be greater?

The energy required is mcpΔT, which will be the same in both cases. This is because the cp of an ideal gas does not vary with pressure.

A unit mass of a substance undergoes an irreversible process from state 1 to state 2 while gaining heat from the surroundings at temperature T in the amount of q. If the entropy of the substance is s1 at state 1 and s2 at state 2, the entropy change of the substance Δs during this process is:

The entropy change of the substance Δs during this process is s2 - s1.

Choose the four processes that make up the Carnot cycle.

The four processes that make up the Carnot cycle are isothermal expansion, reversible adiabatic expansion, isothermal compression, and reversible adiabatic compression.

A mercury manometer (ρ = 13,600 kg/m3) is connected to an air duct to measure the pressure inside. The difference in the manometer levels is 60 mm, and the atmospheric pressure is 100 kPa. Judging from the figure, determine if the pressure in the duct is above or below the atmospheric pressure.

The pressure in the duct is above atmospheric pressure.

The total energy of a flowing fluid consists of internal, kinetic, potential, and _____ energies.

The total energy of a flowing fluid consists of internal, kinetic, potential, and flow energies.

Compare the values of the integral ∫21δQ/T for a reversible and an irreversible process between the same end states.

The value of this integral is always larger for reversible processes.

A liquid that is about to vaporize is saturated liquid; otherwise it is compressed liquid.

True

Consider a steady-flow heat exchanger involving two different fluid streams. Under the conditions of no heat and work interactions between the heat exchanger and the surrounding medium, the amount of heat lost by one fluid will be equal to the amount of heat gained by the other.

True

Consider a steady-flow mixing process. Under the conditions of no heat and work interactions between the mixing chamber and the surrounding medium, the energy transported into the control volume by the incoming streams will be equal to the energy transported out of it by the outgoing stream.

True

Energy can be transferred to or from a control volume as heat, various forms of work, and by mass.

True

Kelvin-Planck states that "no heat engine can exchange heat with a single reservoir and produce an equivalent amount of work."

True

The purpose of a refrigerator is to remove heat from a cold medium, whereas the purpose of a heat pump is to supply heat to a warm medium.

True

Energy can be transferred to or from a control volume as heat, various forms of work, and by mass.

True, energy can be transferred to or from a control volume as heat, various forms of work, and mass.

Volume flow rate is the volume flowing through a cross section per unit time.

True, volume flow rate is the volume flowing through a cross section per unit time.

A propane tank is filled with a mixture of liquid and vapor propane. Can the contents of this tank be considered a pure substance?

Yes

Is a quantity whose cyclic integral is zero necessarily a property?

Yes

Is a process that is internally reversible and adiabatic necessarily isentropic?

Yes, a process that is internally reversible and adiabatic is necessarily isentropic. This is because an internally reversible, adiabatic process involves no irreversibilities or heat transfer.

Is it possible to consider the surrounding air in the room, that houses the TV set, as a suitable choice for a thermal energy reservoir?

Yes, the surrounding air in the room that houses the TV set can be considered as a suitable choice for a thermal energy reservoir.

A quasi-equilibrium process is a process during which a system never remains in equilibrium at all times.

false, A process during which a system remains almost in equilibrium at all times is called a quasi-equilibrium process.

Extensive properties do not depend on the size (extent) of the system.

false, Extensive properties depend on the size of the system.

Intensive properties depend on the size (extent) of the system.

false, Intensive properties do not depend on the size (extent) of the system.

The ordinary temperature scale in the English system is rankine.

false, The ordinary temperature scale in the English system is Fahrenheit(ºF).

The pressure relative to an absolute vacuum is called gage pressure.

false, The pressure relative to an absolute vacuum is called absolute pressure.

Choose the forms in which energy can cross the boundaries of a closed system.

heat and work

Which of the following equations can be obtained from hfg, hf, and hg?

hfg = hg − hf

A system that does not exchange any heat with its surroundings is an adiabatic system.

true

Compressibility factor Z represents the deviation from ideal-gas behavior.

true

In the absence of compressed liquid tables, the compressed liquid can be approximated as a saturated liquid at a given temperature.

true

Is the boundary work associated with constant-volume systems always zero?

yes