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Universal Gas Law

The universal gas law relates temperature, pressure, volume and moles of a gas in a single equation.

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Cook Food In A Flash

Cook Food In A Flash

Credit: Robert Lopez
Source: CK-12 Foundation
License: CC BY-NC 3.0

The ideal gas law is an invaluable tool that allows scientists to relate the state of gases to environmental variables such as surrounding temperatures and pressures. The law, however, assumes that all gas molecules are ideal and therefore do not experience intermolecular forces. Despite these limitations, the ideal gas law provides a solid model for gaseous behavior under various conditions.

News You Can Use

  • The ideal gas law is written as:


In this equation, \begin{align*}P\end{align*} is the absolute pressure, \begin{align*}V\end{align*} is the volume of the gas, \begin{align*}n\end{align*} is the amount of gas in moles, \begin{align*}R\end{align*} is the universal gas constant, and \begin{align*}T\end{align*} is the absolute temperature. This equation gives a good approximation when trying to determine how these conditions are related. As an example, if you were to increase the pressure of a gas while keeping the volume constant, the temperature would increase.

  • A pressure cooker takes advantage of gaseous behavior. It is a sealed container that prepares foods faster by cooking them at higher pressures. When cooking food in boiling water in an open vessel, the temperature of both the food and water cannot exceed 100?, water's boiling point. However inside a pressure cooker, water can boil at a higher temperature thanks to the increased vapor pressure that the pot's design supports.The food is heated at a faster rate because the now higher than 100? liquid can transfer heat to the food at a much faster rate. 
  • Credit: Julie Magrow
    Source: http://www.flickr.com/photos/11172002@N05/4323640485
    License: CC BY-NC 3.0

    Water in a pressure cooker can reach 121 ?C [Figure2]

  • Modern pressure cookers have safety release valves that can release pressure when the pressure inside the pot exceeds a pre-determined value. Furthermore, the temperature of the system can be approximated by using the idea gas law.

Show What You Know

  1. In an isobaric process, what variable in the ideal gas law is considered constant?
  2. An adiabatic process is one in which no heat is exchanged in the system. What implications does this have on the ideal gas law listed above?
  3. If the pressure is held constant while the volume of a gas is expanded, how much work is done?

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Image Attributions

  1. [1]^ Credit: Robert Lopez; Source: CK-12 Foundation; License: CC BY-NC 3.0
  2. [2]^ Credit: Julie Magrow; Source: http://www.flickr.com/photos/11172002@N05/4323640485; License: CC BY-NC 3.0

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