Name: gas mixtures and their partial pressures
Uploaded: 2023-09-18T17:11:17.000Z
Duration: 1 min 11 s
Channel: JoVE

Consider a gas inside a container. The pressure exerted by the gas is the sum of the forces exerted due to the molecular collisions between its molecules and the surrounding surface.
A gas with many molecules exerts a higher pressure than a gas with a smaller number of molecules in the same container. So, the pressure from the individual component is called its partial pressure.
Consider a mixture of ideal gases in a container at thermal equilibrium. The total pressure inside the container equals the sum of the partial pressures of its components. This observation is known as Dalton&#39;s law of partial pressures.
Recalling the ideal gas equation and substituting the partial pressures of the individual gases, the total pressure can be determined.
The partial pressure of a vapor which is in equilibrium with the liquid phase of the same substance is called vapor pressure.
The ratio of the partial pressure of water vapor to the vapor pressure of water at a temperature is known as relative humidity.

dalton's law of partial pressure

Dalton's Law of Partial Pressure

The partial pressure of a gas is a measure of the thermodynamic activity of the gas&#39;s molecules. The pressure that a gas would create if it occupied the total volume available is called the gas&#39;s partial pressure. If two or more gases are mixed together in a container, the molecules move randomly and collide with each other, causing them to reach thermal equilibrium. When the gases have the same temperature, their molecules have the same average kinetic energy. Thus, each gas obeys the ideal gas law separately and exerts the same pressure on the walls of a container individually. Therefore, in a mixture of gases, the total pressure in the container is the sum of the partial pressures of the component gases, assuming ideal gas behavior and no chemical reactions between the components. This law is known as Dalton&#39;s law of partial pressures. The theory was established by the English scientist John Dalton (1766&#8211;1844). Dalton&#39;s law is consistent with the fact that pressures add up, according to Pascal&#39;s principle. In a mixture of ideal gases in thermal equilibrium, the number of molecules of each gas is proportional to its partial pressure.
Another important application of partial pressure is vapor pressure, which is the partial pressure of a vapor at which it is in equilibrium with the liquid phase of the same substance. At any temperature, the partial pressure of the water in the air cannot exceed the vapor pressure of the water at that temperature, as whenever the partial pressure reaches the vapor pressure, water condenses out of the air. Dew is an example of this condensation. The temperature at which condensation occurs for a sample of air is called the dew point. It is easily measured by slowly cooling a metal ball; the dew point is the temperature at which condensation first appears on the ball.

The partial pressure of a gas is a measure of the thermodynamic activity of the gas&#39;s molecules. The pressure that a gas would create if it occupied ...

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JoVE Core

Physics

Unit 1

The Kinetic Theory of Gases

KEY TERMS AND CONCEPTS

gas mixtures and their partial pressures

Gas mixtures have a total pressure that comes from the partial pressures of each gas. A partial pressure is the pressure one gas would make if it filled the whole container by itself. This idea helps explain how gases behave when they are mixed together.

When two or more gases share a container, their molecules move randomly and collide with one another. If the gases are at the same temperature, they reach thermal equilibrium. Their molecules then have the same average kinetic energy. In that case, each gas follows the ideal gas law separately and pushes on the walls of the container on its own.

The total pressure in the container is the sum of the partial pressures of the component gases. This result is called Dalton's law of partial pressures. It applies when the gases behave like ideal gases and do not react chemically with one another. The law was developed by the English scientist John Dalton, who lived from 1766 to 1844. It also agrees with Pascal's principle, which says that pressures add up.

Partial pressure also helps describe vapor pressure. Vapor pressure is the partial pressure of a vapor when it is in equilibrium with the liquid form of the same substance. In air, the partial pressure of water cannot rise above the vapor pressure of water at that temperature. If it reaches that value, water condenses out of the air. Dew is one common example of this process.

The temperature where condensation begins in a sample of air is called the dew point. One simple way to measure it is to cool a metal ball slowly. The dew point is the temperature at which condensation first appears on the ball.

Gas Mixtures and Their Partial Pressures

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maxwell-boltzmann-distribution-problem-solving

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Gas collisions: path length and time

Gas collisions in a cylinder help explain the mean free path and mean free time. Gas molecules move in random motion. They collide with each other and change speed and direction. The mean free path is the average path length between collisions. The mean free path depends on how many molecules are packed into a volume. It varies inversely with density. When more molecules are present, collisions happen more often, so the mean free path becomes shorter. It also depends on molecule size. Larger...

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Gas mixtures have a total pressure that comes from the partial pressures of each gas. A partial pressure is the pressure one gas would make if it filled the whole container by itself. This idea helps explain how gases behave when they are mixed together. When two or more gases share a container, their molecules move randomly and collide with one another. If the gases are at the same temperature, they reach thermal equilibrium. Their molecules then have the same average kinetic energy. In that...

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key terms and concepts

Learn how gas mixtures share pressure through partial pressures, how Dalton's law works, and how vapor pressure and dew point explain condensation in air.

Gas Mixtures and Their Partial Pressures | JoVE K12

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Gas Mixtures and Their Partial Pressures

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