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Ch.18 - Chemistry of the Environment
Chapter 18, Problem 12

From the data in Table 18.1, calculate the partial pressures of carbon dioxide and argon when the total atmospheric pressure is 1.05 bar.

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1
Identify the components of the mixture: carbon dioxide (CO₂) and argon (Ar).
Understand that the total pressure is the sum of the partial pressures of the gases present: \( P_{\text{total}} = P_{\text{CO}_2} + P_{\text{Ar}} \).
Use the mole fraction of each gas to determine its partial pressure. The partial pressure of a gas is given by \( P_i = X_i \times P_{\text{total}} \), where \( X_i \) is the mole fraction of the gas.
Look up or calculate the mole fractions of CO₂ and Ar from Table 18.1. If the table provides mole fractions, use them directly. If it provides percentages, convert them to mole fractions by dividing by 100.
Calculate the partial pressures: \( P_{\text{CO}_2} = X_{\text{CO}_2} \times 1.05 \text{ bar} \) and \( P_{\text{Ar}} = X_{\text{Ar}} \times 1.05 \text{ bar} \).

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Key Concepts

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

Dalton's Law of Partial Pressures

Dalton's Law states that in a mixture of gases, the total pressure exerted is equal to the sum of the partial pressures of each individual gas. This principle allows us to calculate the pressure of a specific gas in a mixture by knowing the total pressure and the mole fraction of that gas.
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Mole Fraction

The mole fraction is a way of expressing the concentration of a component in a mixture. It is defined as the ratio of the number of moles of a specific gas to the total number of moles of all gases in the mixture. This value is crucial for calculating the partial pressure of each gas using Dalton's Law.
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Ideal Gas Law

The Ideal Gas Law relates the pressure, volume, temperature, and number of moles of a gas through the equation PV = nRT. While this law is not directly used for calculating partial pressures, it provides a foundational understanding of gas behavior and can help in determining the number of moles needed for calculating mole fractions.
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