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Charles's Law (Law of Volumes)

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  • Charles' Law

    For a fixed mass of gas at constant pressure, the volume is directly proportional to temperature (in Kelvin). This is mathematically

    \[ V = constant x T \]

    That means, for example, that if you double the temperature from, say to 300 K to 600 K, at constant pressure, the volume of a fixed mass of the gas will double as well. You can express this mathematically as

    Is this consistent with pV = nRT ?

    • You have a fixed mass of gas, so n (the number of moles) is constant.
    • R is the gas constant.
    • Charles' Law demands that pressure is constant as well.

    If you rearrange the pV = nRT equation by dividing both sides by p, you will get

    V = nR/p x T

    But everything in the nR/p part of this is constant. That means that V = constant x T, which is Charles' Law.

    Contributors and Attributions

    Jim Clark (

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