Find the change in pressure

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Homework Statement


Two balloons are connected by a faucet.
Gas in the first balloon is at pressure [itex]p_1=100kPa[/itex], and in the second is [itex]p_2=0,5MPa[/itex].
Volumes are [itex]V_1=0,12m^3[/itex] and [itex]V_2=0,5m^3[/itex].
Temperature of a gas is constant.
Find pressure in balloons [itex]p[/itex] after faucet is opened (balloons are not connected).

Homework Equations


[itex]pV=\frac{m}{M}RT[/itex] - state of ideal gas

The Attempt at a Solution


State of gas before before balloons are disconnected is
[itex]p_1V_1=\frac{m}{M}RT,p_2V_2=\frac{m}{M}RT[/itex]
and after balloons are disconnected is
[itex]p(V_1+V_2)=\frac{2mRT}{M}\Rightarrow p=\frac{2p_1p_2}{p_1+p_2}=166,67kPa[/itex].

Is this correct? How volumes [itex]V_1[/itex] and [itex]V_2[/itex] are not relevant in the equation for [itex]p[/itex]?
 

Answers and Replies

  • #2
haruspex
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##p_1V_1=\frac{m}{M}RT,p_2V_2=\frac{m}{M}RT##
Are m and M the same for both?
 
  • #3
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Are m and M the same for both?
Mass of a balloon [itex]m[/itex] and atomic mass [itex]M[/itex] are not given. Could you elaborate how to set the equations
for finding the pressure [itex]p[/itex] in second case (disconnected balloons)?
 
  • #4
haruspex
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Mass of a balloon [itex]m[/itex] and atomic mass [itex]M[/itex] are not given. Could you elaborate how to set the equations
for finding the pressure [itex]p[/itex] in second case (disconnected balloons)?
You can assume M is the same for both, but not m. Assign two different unknowns. You have enough equations to cope with that.
 
  • #5
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I'm not sure as I'm only just learning this stuff myself though it appears I'm a couple of weeks behind you but wouldn't it be worth finding the mass flow rate? Sorry if that's wrong.
 
  • #6
haruspex
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I'm not sure as I'm only just learning this stuff myself though it appears I'm a couple of weeks behind you but wouldn't it be worth finding the mass flow rate? Sorry if that's wrong.
I read the question as asking about the final state, after flow has ceased and temperatures have returned to ambient.
(Otherwise there is not enough information.)
 

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