# Find the change in pressure

## Homework Statement

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).

## Homework Equations

$pV=\frac{m}{M}RT$ - state of ideal gas

## 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 $p$?

haruspex
Homework Helper
Gold Member
2020 Award
##p_1V_1=\frac{m}{M}RT,p_2V_2=\frac{m}{M}RT##
Are m and M the same for both?

Are m and M the same for both?
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)?

haruspex
Homework Helper
Gold Member
2020 Award
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)?
You can assume M is the same for both, but not m. Assign two different unknowns. You have enough equations to cope with that.

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.

haruspex