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What is the entropy if you have a spray can with 30psi?

  1. Nov 23, 2012 #1
    I am asking this question because I am trying to understand what entropy is and I just can't seem to get it clear.

    Now I think the asnwer is 0.5.
    The pressure of the can is 30.
    the Atmospheric pressure is around 15.
    You devide the pressure in the can by the atmospheric pressure and you have the entropy.

    So first question is, is that right?
    Second question is what is the system?
    Is the system the can or the can and the atmospheric pressure or just the atmosheric pressure?
  2. jcsd
  3. Nov 23, 2012 #2
    ...No. I don't know where you got the idea that entropy is the quotient of two pressures. And, even then, [itex]\frac{30}{15} = 2 \neq 0.5[/itex].

    Entropy is a measure of disorder and randomness in a system. It can be calculated using the Gibbs entropy formula, [itex]S = -k_{B} \displaystyle\sum_{i} p_{i}\ln{p_{i}}[/itex], where S denotes entropy, and [itex]k_{B}[/itex] is the Boltzmann constant. One could also use [itex]S = k_{B} \ lnΩ[/itex], where Ω denotes the number of microstates consistent with the given macrostate.
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