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A gas mixture contains 10.0 mole \(\% \mathrm{H}_{2} \mathrm{O}(\mathrm{v})\) and 90.0 mole \(\% \mathrm{N}_{2} .\) The gas temperature and absolute pressure at the start of each of the three parts of this problem are \(50^{\circ} \mathrm{C}\) and \(500 \mathrm{mm}\) Hg. Ideal-gas behavior may be assumed in every part of this problem.(a) If some of the gas mixture is put in a cylinder and slowly cooled at constant pressure, at what temperature would the first drop of liquid form?(b) If a 30.0 -liter flask is filled with some of the gas mixture and sealed and \(70 \%\) of the water vapor in the flask is condensed, what volume \(\left(\mathrm{cm}^{3}\right)\) would be occupied by the liquid water? What would be the system temperature?(c) If the gas mixture is stored in a rigid-walled cylinder and a low-pressure weather front moves in and the barometric (atmospheric) pressure drops, which of the following would change: (i) the gas density, (ii) the absolute pressure of the gas, (iii) the partial pressure of water in the gas, (iv) the gauge pressure of the gas, (v) the mole fraction of water in the gas, (vi) the dew-point temperature of the mixture?

Short Answer

Expert verified
The dew point temperature will be found looking up a water vapor saturation pressure table. The liquid water volume can be calculated through identifying the moles of water in the flask and using the properties of water (density, molar mass). Changes due to reduction in barometric pressure will vary based on their dependence on pressure, if the volume of the mixture is constant.

Step by step solution

01

Determination of dew point temperature

First, the dew point temperature of the gas mixture needs to be determined. The dew point is the temperature at which condensation starts as the gas mixture is cooled. We need to look up or calculate the saturation pressure of water vapor at 50C, and convert this to a percentage of the total pressure (500mmHg). This percentage is equivalent to the mole fraction of water (10%), so we can then find the dew point temperature of the mixture where the saturation pressure of water equals 10% of the total pressure.
02

Calculation of water condensation volume

Next, in part (b), the problem states that 70% of the water vapor in the flask condenses. First we'll calculate the total moles of the gas in the flask using the ideal gas law, PV = nRT, and using this to find the moles of water vapor. We can then use the fact that 70% of this water condenses to a liquid. This is equivalent to multiplying the moles of water vapor with mole percentage and 0.70 to get the moles of liquid water. Knowing that the density of water is 1g/cm3 and its molar mass is 18.015g/mol, we can use these to calculate volume in cm3.
03

Response to atmospheric pressure change

Finally, for part (c), we examine how changes in barometric pressure would affect various properties of the gas. Given that the cylinder is rigid, the volume of gas won't change, allowing us to infer the influence on gas density, absolute pressure, partial pressure of water, gauge pressure, mole fraction of water, and dew-point temperature. Understanding the principles of the ideal gas behavior and the relation between pressure and the properties aforementioned is crucial in answering these.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Dew Point Temperature
The dew point temperature is a key concept in understanding how condensation occurs in a gas mixture. It is the temperature at which water vapor in the air starts to condense into liquid water. In this exercise, the challenge is to find out the temperature at which the first drop of liquid forms when cooling a gas mixture of water vapor and nitrogen.

To calculate the dew point temperature, you need to understand the relationship between the saturation pressure of water vapor and its mole fraction in the mixture. At 50°C, we first determine the saturation pressure of water vapor. This pressure relates to how much water vapor can be held by the air at a given temperature.

Then, by assuming ideal gas behavior, we set the partial pressure of the water vapor (which is 10% of the total pressure) equal to this saturation pressure. This allows us to identify the dew point as the temperature where these two pressures meet.

In essence, when the ambient temperature falls below the dew point temperature, the excess water vapor condenses into liquid. This understanding helps handle practical applications such as weather forecasting and designing HVAC systems.
Partial Pressure
Partial pressure plays a pivotal role in gas mixtures within the context of the ideal gas law. It represents the pressure exerted by a single component in a mixture of gases. Each gas in a mixture behaves independently and contributes to the total pressure based on its proportion.

In our gas mixture of water vapor and nitrogen, partial pressure is critical to solving for the dew point and assessing condensation. Given 10% mole fraction of water vapor, its partial pressure is 10% of the total 500 mmHg pressure. Knowing each component's partial pressures allows you to predict how the gas behaves when it is cooled or pressured changes.

Partial pressure is beneficial to determine how gases dissolve, react, or condense in diverse conditions. In real-world scenarios, understanding partial pressure is critical for predicting chemical reactions, respiratory exchange processes, and even culinary practices like carbonation.
Gas Mixture Properties
The physical properties of gas mixtures are vital to solving problems involving ideal gas law concepts. In this exercise, understanding these properties allows us to analyze how the mixture behaves when subjected to temperature and pressure changes.

Gas mixtures like our water vapor and nitrogen example exhibit properties such as total pressure, component volume, and the overall density, derived from their individual gas properties and interactions. In the context of ideal gases, we assume no interactions between molecules, allowing us to simplify calculations using laws like Dalton’s Law of Partial Pressures.

When atmospheric conditions change, such as a reduction in pressure due to weather fronts, assessing gas mixture properties helps predict changes in dew point temperature, pressure distributions, and even volume if the container geometry isn’t rigid.

Comprehending gas mixture properties enables practical insights into industrial applications, air conditioning systems, and even environmental science, where these fundamental principles are often applied.

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Most popular questions from this chapter

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