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Thermodynamical state

  1. Dec 27, 2011 #1
    Hi All,
    During my study of thermodynamics these days I have a little confusion regarding the concept of state of a system and state functions. Here I begin what confuses me.
    We know temperature, pressure, volume, internal energy, entropy etc. are state functions. 1.I am wondering if a system at a particular state has some unique values of state functions?
    2. What does it really mean by a state of a thermodynamic system?
    3.Can two simillar systems at same state have different internal energy? OR Do internal energy is some special type of state function, which could indepedently clearifies what is the state of the system.
    4. Is it possible for any process ,(to occur) where the initial and final state are different though the change internal energy is zero.
    In short the concept of state confuses me. Any help will be highily appreciated.
  2. jcsd
  3. Dec 27, 2011 #2

    Simon Bridge

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    That's sort-of correct.
    The physical "state" of a system is the condition it is in.
    Like when you come in muddy and someone says "Look at the state you are in!" Your state is your physical condition.

    We represent a thermodynamic state mathematically as a set of numbers - when we have enough numbers that, from them, we can determine everything we need to know about the system, then we have a complete description of it's state. We will often refer to the set of numbers as the state as a kind of shorthand.

    Classically, the state of an ideal gas is completely described by it's volume, pressure, and temperature (and the number of molecules).

    You should be able to figure this out from the previous - you know how to find the internal energy of a system from it's state variables: does that relationship allow more than one value for a given state?

    Of course - but you know this one too: the thermodynamic processes are adiabatic, isobaric, isothermal and isochoric. You have the internal energy relations for each one - which is/are zero?
  4. Dec 27, 2011 #3
    Thanks you so much Simon Bridge, I really got benifitted by your answers. Here one more thing I want to get clearified...
  5. Dec 27, 2011 #4
    Suppose i have two containers of raw rice of same hybrid (i.e having same internal energy) and i started cooking them using same ingridents but by different mode of heating. If after being cooked to the same level it is found that the change in internal energy in both is the same, now is it necessary that they would be of same taste and having same final temperature? thanks!!
  6. Dec 27, 2011 #5

    Simon Bridge

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    Taste is not a thermodynamic property.

    Cooking is not exact, and neither is taste.
    As a result, it is quite easy to make two bowls of rice taste sufficiently the same that many independent diners will agree "they taste the same!"

    We don't usually have or need a complete description of the state of something to be able to do useful things with it.
  7. Dec 27, 2011 #6
    Ok.., means by just knowing the internal energy of a paeticular well known sysrem, one can not pridict other state functions(their values), the system is in. Can this be finally assumed?
    Or i can say two systems undegoes same change in internal energy from same initial state may have diffetent final temperature. WITH REGARDS!!
    Last edited: Dec 27, 2011
  8. Dec 27, 2011 #7
    I will further be very thankfull to anybody who could tell me that, if two systems(similar) are at same state, will that mean that all the state functions will have the same value or not? I really very curious to understant. I am sorry for my dull mind:)
  9. Dec 27, 2011 #8

    Simon Bridge

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    Sure - the configuration of a system, even something like an ideal gas, can lead to different states with the same internal energy.

    One of the things worth studying as you progress through life is how little information you need before you know everything about the system ... and how little you need to know to do something useful with it.

    And an inquiring mind is seldom dull - at least not for long.
  10. Dec 28, 2011 #9
    Thanks I understood the matter now.Love to have more discussions in future. Thanks again:)
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