Q: Relative humidity is defined as:

$$\%RH = \frac{P_{vapor}}{P_{vapor}^0} \times 100$$

Question 1

In a gas-liquid system with one condensable component, which condition must be met for the vapor phase to be considered saturated?

Accepted Answer

The partial pressure of the vapor equals the vapor pressure at the system temperature.

Question 2

Which equation correctly expresses Raoult’s Law for a single condensable species in a gas-liquid system?

Accepted Answer

$$P_{vapor} = y_{vapor} P$$

Question 3

Relative humidity is defined as:

Accepted Answer

$$\%RH = \frac{P_{vapor}}{P_{vapor}^0} 	imes 100$$

Question 4

A mixture of benzene and air at 36°C and 100 kPa has a dew point of 16°C. What does the dew point represent in this context?

Accepted Answer

The temperature at which benzene just starts to condense from the vapor phase.

Question 5

Which formula is used to calculate molal humidity (molal saturation) in a gas-vapor system?

Accepted Answer

$$MS(H) = \frac{n_{vapor}}{n_{dry\ gas}}$$

Question 6

In a closed container at 25°C and 120 kPa, 250 grams of steam is injected into 55 kg of air. Which step is necessary to calculate the percent relative humidity?

Accepted Answer

Calculate the partial pressure of water vapor and compare it to the vapor pressure at 25°C.

Question 7

Absolute humidity (AS(H)) can be expressed as:

Accepted Answer

$$AS(H) = \frac{mass_{vapor}}{mass_{dry\ gas}}$$

Question 8

Percent saturation (percent humidity) is calculated using which formula?

Accepted Answer

$$\%S(H) = \frac{P_{vapor}}{P^0$} \frac{P - P^0$}{P - P_{vapor}} 	imes 100$$

Question 9

If the partial pressure of water vapor in a system is less than the vapor pressure at the system temperature, what is the state of the vapor?

Accepted Answer

The vapor is unsaturated.

Question 10

Which of the following best describes the dew point in a mixture of pure vapor and non-condensable gas?

Accepted Answer

The temperature at which the vapor just starts to condense.

Question 11

A gas phase is saturated with water at a given temperature and pressure. What does this imply about the partial pressure of water vapor?

Accepted Answer

It is equal to the vapor pressure of water at that temperature.

Question 12

In a real-world scenario, why is it important to know the dew point when designing air conditioning systems?

Accepted Answer

To prevent condensation and water damage in the system.

Question 13

Which of the following is NOT a correct step in calculating the composition by volume of benzene in air given the dew point and total pressure?

Accepted Answer

Use the mass of air to directly calculate the mole fraction of benzene.

Question 14

Which real-life application relies on the concept of percent saturation (percent humidity)?

Accepted Answer

Designing industrial dryers for pharmaceuticals.

Question 15

If the absolute humidity in a system increases, what is the most likely effect on the dew point?

Accepted Answer

The dew point increases.

Question 16

Which of the following equations is used to calculate the mass of vapor in a gas mixture using absolute humidity?

Accepted Answer

$$mass_{vapor} = AS(H) 	imes mass_{dry\ gas}$$

Question 17

In a gas-liquid system, what does equilibrium between the liquid and vapor phases imply?

Accepted Answer

No net exchange of liquid and vapor.

Question 18

Which parameter is most critical for determining whether condensation will occur in a gas-vapor mixture?

Accepted Answer

Partial pressure of the vapor compared to its vapor pressure at the system temperature.

Question 19

A chemical engineer needs to calculate the molal humidity in a process stream. Which data is essential for this calculation?

Accepted Answer

Number of moles of vapor and number of moles of dry gas.

Gas-Liquid Systems: One Condensable Component & Humidity Calculations

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