Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Heating a gas at constant pressure

  1. May 17, 2006 #1
    Sir,
    Please help me with this problem.
    A Volume – Temperature diagram was obtained when a gas was heated at a constant pressure. During the heating process from state 1 to state 2 how does its mass vary?
    Sometimes the diagram may not clear, so I will try to describe how it looks like. It is a straight line graph with an inclination of around 30 degrees. It has a positive slope. The volume is along the Y axis and the temperature is along the X axis.
    I solved it the following way:
    From the graph it is clear that at any point on the graph V/T < 1
    But according to gas law,
    PV = wRT/m
    Where w = mass of gas and m = Molecular weight of gas
    i.e. V/T proportional to w ( Since P is constant)
    i.e. w < 1
    Hence the mass of the gas decreases. Though it agrees with the answer in my book, I don’t know whether it is right. Please say whether its right or not?
     

    Attached Files:

  2. jcsd
  3. May 18, 2006 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Not quite. The graph is a straight line. What does that tell you about how V varies with T?

    Now apply the ideal gas law: PV=nRT or V = nRT/P

    If P is constant and the graph of V vs. T is linear, can n vary at all?

    AM
     
  4. May 18, 2006 #3
    Sir,
    So do you mean that as V/T is a constant and moreover pressure being constant, mass of gas is constant?
     
  5. May 18, 2006 #4

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    You got it.

    AM
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook