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14 Cards in this Set

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3. Somebody claims that the mass fraction and the mole fractions for a mixture of CO2 and N20 gases are identical, Is this true? Why?

Yes, it is true because the molar masses of CO2 (44) g/mol and N2O (44) g/mol are identical, the mass fractions and mole fractions of the individual components will always equal each other.
17. Consider a rigid tank which contains a mixture of two ideal gases. A valve is opened and some gas escapes. As a result, the pressure in the tank drops. Will the partial pressure of each component change? How about the pressure fraction of each component?
Partial pressure will change since pi=xi*P where xi is the mole fraction of the individual component, and P is the total pressure. Since the total pressure changes, pi will as well. Pressure fraction will stay the same.
18. Consider a rigid tank which contains a mixture of two ideal gases. The gas mixture is heated and the pressure and the temperature in the tank rise. Will the partial pressure of each component change? How about the pressure fraction of each component?
The partial pressure and pressure fractions will not change. As the pressure changes the partial pressures and fraction will remain the same.
30. Explain how a real–gas mixture can be treated as a pseudopure substance using Kay's Rule.
It involves the use of pseudocritical pressure P' and pseudocritical temperature T' for the mixture, defined in terms of the critical pressures and temperatures of the mixture components. P' = sum of YiPci and T'= sum of yiTci or Prm=(P/Pcm) and Trm=(T/Tcm)
32. Can the water vapor in the air be treated as an ideal gas? Explain.
Yes it can be treated as an ideal gas without much error. Find the z value to confirm this, or compare the specific volumes.Fix this
36. How will (a) the humidity ratio and (b) relative humidity of the air contained in a well-sealed room change if it is heated?

(a) the humidity ratio is not dependent on the temperature (b) The amount of moisture air can hold depends on its temperature, therefore the relative humidity of air changes with temperature even when its humidity ratio remains constant. As the temperature increases, so does the relative humidity.

37. Is it possible to obtain saturated air from unsaturated air without adding any moisture? Explain.
Yes, cool it to the dew point temperature while at constant pressure.
41. Ann and Andy both wear glasses. On a cold winter day, Ann comes in from the cold outside and enters the warm house while Andy leaves the house and goes outside. Whose glasses are more likely to be fogged? Explain.
Ann's glasses are more likely to fog because the temp of her glasses will more likely be lower than the dew point temperature of the air inside the warm house, which will cause condensation
42. In summer, the outer surface of a glass filled with iced water frequently “sweats.” How can you explain this sweating?
Sweating is dew that forms on the drink, this indicates the temp of the drink is below the dew point temp of the surrounding air
43. In some climates, cleaning the ice off the car windows is a common chore on winter mornings. Explain how ice forms on the car windows during some nights even when there is no rain or snow.
The windshield radiates heat to the far sky which cools the windshield below the dew point of the surrounding air causing condensation which then freezes.
47. A house contains air at 80°F and 65% relative humidity. Will any moisture condense on the inner surfaces of the windows when the temperature of the window drops to 50°F? Explain.
Psat = 3.2kPa Pv=(.65)(3.2)=2.1kPa Tdp = Tsat@2.1kPa = 65°F; The new saturation temp is above the window temp so there will be condensation.
48. After a long walk in the 12°C outdoors, a person wearing glasses enters a room at 25°C and 40% relative humidity. Determine whether the glasses will become fogged.
The dew point temperature is 11°C, since the temperature of the persons glasses is higher than the dew point temperature, there will not be any condensation.FIX THIS
54. How is the dew-point temperature at a specified state determined on the psychrometric chart?

The dew point temp is determined by drawing a horizontal line from the specific state to the left until it intersects the saturation line.

55. Can the enthalpy values determined from a psychrometric chart at sea level (one atmosphere pressure) be used at higher elevations?

No, you have to use different psychrometric charts for pressures considerably different than atmospheric pressure at sea level, because the enthalpy of water vapor is dependent on pressure.