# Find the change in pressure

1. Feb 25, 2016

### gruba

1. The problem statement, all variables and given/known data
Two balloons are connected by a faucet.
Gas in the first balloon is at pressure $p_1=100kPa$, and in the second is $p_2=0,5MPa$.
Volumes are $V_1=0,12m^3$ and $V_2=0,5m^3$.
Temperature of a gas is constant.
Find pressure in balloons $p$ after faucet is opened (balloons are not connected).

2. Relevant equations
$pV=\frac{m}{M}RT$ - state of ideal gas

3. The attempt at a solution
State of gas before before balloons are disconnected is
$p_1V_1=\frac{m}{M}RT,p_2V_2=\frac{m}{M}RT$
and after balloons are disconnected is
$p(V_1+V_2)=\frac{2mRT}{M}\Rightarrow p=\frac{2p_1p_2}{p_1+p_2}=166,67kPa$.

Is this correct? How volumes $V_1$ and $V_2$ are not relevant in the equation for $p$?

2. Feb 25, 2016

### haruspex

Are m and M the same for both?

3. Feb 25, 2016

### gruba

Mass of a balloon $m$ and atomic mass $M$ are not given. Could you elaborate how to set the equations
for finding the pressure $p$ in second case (disconnected balloons)?

4. Feb 25, 2016

### haruspex

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. Feb 25, 2016

### JustDerek

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. Feb 25, 2016

### haruspex

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.)