# Need help using Ideal Gas Law

## Homework Statement

A rigid tank contains 5 kg of an ideal gas at 4 atm and T=40 deg C. Now, a valve is opened and half of the mass of the gas is allowed to escape. If the final pressure in the tank is 1.5 atm, the final temperature in the tank is?

pV=mRT

## The Attempt at a Solution

I know pV=mRT but I don't know how to use this equation for to different states i.e. beginning and end state.

vela
Staff Emeritus
Homework Helper
The equation holds for the two different states, so you have
\begin{align*}
p_i V_i &= m_i R T_i \\
p_f V_f &= m_f R T_f
\end{align*}
What are the quantities you know? What other relationship were you given that relates the quantities?

That is it. That is the whole problem statement. No specific gas or fluid was given.

vela
Staff Emeritus