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    Quick question,

    internal energy = Ek + Ep

    So if we increase the potential energy of a gas, we increase the internal energy right?

    But what exactly does an increase in potential energy mean?

    Is it an increase in distance between two molecules/atoms?

    Its so confusing
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    Go back to pressure, volume and temperature.

    Pressure is force/unit area, temperature is a measure of the kinetic energy of the gas. So if you change one parameter by doing work on the gas, what happens to the others?
    What does that mean for the kinetic energy and hence the stored potential energy?
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    An ideal gas doesn't have potential energy. PE is due to intermolecular forces.

    BUT

    PE is negative - the stronger the forces are the lower the PE.
    That's why you have to supply energy to break bonds. To get back to a zero energy state.
    Ultimately it because of the way we define zero PE.
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    (Original post by teachercol)
    An ideal gas doesn't have potential energy. PE is due to intermolecular forces.

    BUT

    PE is negative - the stronger the forces are the lower the PE.
    That's why you have to supply energy to break bonds. To get back to a zero energy state.
    Ultimately it because of the way we define zero PE.
    So does that mean a closer two molecules are the larger the PE?
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    If molecules are close together , the PE is more negative - its prop to -1/r

    its confusing referring to larger and smaller.

    Is -1 bigger than -2 or smaller?
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    (Original post by teachercol)
    If molecules are close together , the PE is more negative - its prop to -1/r

    its confusing referring to larger and smaller.

    Is -1 bigger than -2 or smaller?
    Well I guess it's magnitudeally bigger but vectorically smaller? :P

    Well this brings me to the point

    If internal energy = Ep + Ek
    And an increasing temperature means an increase in internal energy

    Surely that means even during phase change, T should increase because Ep is increasing ( i.e. getting less negative )


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    (Original post by kinglynx)
    Well I guess it's magnitudeally bigger but vectorically smaller? :P

    Well this brings me to the point

    If internal energy = Ep + Ek
    And an increasing temperature means an increase in internal energy

    Surely that means even during phase change, T should increase because Ep is increasing ( i.e. getting less negative )


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    True enough, adding heat will increase internal energy. However, increasing Ep does not imply increasing T.

    Temperature depends on kinetic energy, as in the equation E = \frac{3}{2}kT where E is the mean translational kinetic energy of a particle in the gas.

    Increased potential energy means increased separation and disorder. If work must be done to break bonds and thus separate particles, then their potential energy has increased.

    By the way, in my opinion 'increasing potential energy' is not ambiguous, it means more positive. We really care about changes in potential energy, so don't worry about the fact that it is defined as negative.
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    (Original post by Brister)
    True enough, adding heat will increase internal energy. However, increasing Ep does not imply increasing T.

    Temperature depends on kinetic energy, as in the equation E = \frac{3}{2}kT where E is the mean translational kinetic energy of a particle in the gas.

    Increased potential energy means increased separation and disorder. If work must be done to break bonds and thus separate particles, then their potential energy has increased.

    By the way, in my opinion 'increasing potential energy' is not ambiguous, it means more positive. We really care about changes in potential energy, so don't worry about the fact that it is defined as negative.
    I get 100% what your saying. But how come my statement is falsified?

    If IE = Ep + Ek, and T ∝ IE, then sureley Ep ^ means IE ^ means T ^?
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    (Original post by kinglynx)
    I get 100% what your saying. But how come my statement is falsified?

    If IE = Ep + Ek, and T ∝ IE, then sureley Ep ^ means IE ^ means T ^?
    Temperature is not proportional to internal energy; it is only proportional to kinetic energy.
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    (Original post by Brister)
    Temperature is not proportional to internal energy; it is only proportional to kinetic energy.
    Hmm thats odd this sheet of notes i got from my physics teacher said the hotter an object is, the higher the temperature and temperature depends on internal energy which in turn depends on Ek and Ep

    but if its as simple as that then awesome

    thanks man
 
 
 
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