The percent by volume of oxygen (20.95%) is constant throughout the troposphere. (a) Express this percentage as a mole fraction.

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Start by understanding that percent by volume is equivalent to percent by mole fraction for gases under the same conditions.

Convert the percentage to a decimal by dividing by 100: 20.95% becomes 0.2095.

Recognize that the mole fraction of oxygen is the ratio of moles of oxygen to the total moles of gas.

Since the percentage by volume is equivalent to the mole fraction, the mole fraction of oxygen is 0.2095.

Conclude that the mole fraction of oxygen in the troposphere is 0.2095, as the percentage by volume directly translates to mole fraction for gases.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Percent by Volume

Percent by volume is a way of expressing the concentration of a component in a mixture, defined as the volume of the component divided by the total volume of the mixture, multiplied by 100. In the context of gases, it indicates the proportion of a specific gas in the atmosphere, which helps in understanding its relative abundance compared to other gases.

Mole Fraction

Mole fraction is a dimensionless quantity that represents the ratio of the number of moles of a specific component to the total number of moles of all components in a mixture. It is calculated by dividing the moles of the component by the total moles, providing a useful way to express concentrations in chemical reactions and gas mixtures.

Ideal Gas Law

The Ideal Gas Law relates the pressure, volume, temperature, and number of moles of an ideal gas through the equation PV = nRT. This law is fundamental in understanding gas behavior and allows for the conversion between different measures of concentration, such as percent by volume and mole fraction, especially in atmospheric chemistry.

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Textbook Question

Name the regions of the atmosphere. What property is used to distinguish between different regions of the atmosphere?

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Textbook Question

The Earth's atmosphere has a mass of approximately 5.15 * 1015 kg. If the average molar mass of air is 28.8 g/mol, how many moles of gas make up the atmosphere? What is the volume of the atmosphere in liters under conditions of STP? (Note: The average molar mass of air is the weighted average of the molar mass of nitrogen and oxygen. 0.20132.0 g>mol2 + 0.80128.0 g>mol2 = 28.8 g>mol.)

Textbook Question

The troposphere contains about three quarters of the mass of the entire atmosphere. The troposphere is only 12 km thick while the whole atmosphere is about 120 km thick. Explain why the troposphere contains such a large fraction of the total mass.

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