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Combined Gas Law

Volume, temperature and pressure are interrelated qualities of gases.

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Practice Combined Gas Law
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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

Even though there are several limitations, the ideal gas law serves as a good approximation when attempting to approximate the behavior of gases under various conditions.

News You Can Use

  • The ideal gas law is known as


Where P is the absolute pressure, V is the volume of the gas, n is the amount of gas in moles, R is the universal gas constant and T is the absolute temperature. This equation gives a good approximation when trying to determine how each of the variables in a gas is related. As an example, if you were to increase the pressure of a gas under constant volume, the temperature would increase.

  • A pressure cooker is a device that cooks food while not allowing liquid or air to escape during the cooking process. The food is heated at a faster rate because the internal pressure from the boiling liquid causes a much higher temperature water vapor to transfer heat in the system. Because less liquid is needed compared to most conventional cooking methods, pressure cookers allow food to be cooked faster. 
  • Credit: Julie Magrow
    Source: http://www.flickr.com/photos/11172002@N05/4323640485
    License: CC BY-NC 3.0

    A pressure cooker allows food to be cooked at a faster rate [Figure2]


  • Since most modern pressure cookers have safety release valves that release some of the pressure at pre-determined values, the temperature of the system can be monitored by using the idea gas law as an approximation.

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?

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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