# Homework Help: Ideal Gas Law and a helium tank

1. Jan 24, 2009

### gabriel5

1. The problem statement, all variables and given/known data
Helium in a steel tank is at 250kPa, 300K with a volume of .1m^3. It is used to fill a balloon. When the pressure drops to 150kPa, the flow of helium stops by itself. If all the helium is still at 300k, how big balloon is produced?

2. Relevant equations
I used the ideal gas law PV=mRT

3. The attempt at a solution
What i did was that i solved for the mass which i got was .04012 and then i used that mass in the ideal gas law with the new pressure of 150kPa to get a new volume of .167 m^3 is this the right approach and answer?

2. Jan 25, 2009

### Staff: Mentor

That's a fine approach, but be sure to answer the precise question asked: How big is the balloon?

Rather than calculate the mass, since it's constant, you could have just used:
P1V1 = P2V2.

3. Jan 25, 2009

### gabriel5

By asking how big the balloon is doesn't it mean give the volume or what do you think i should put down?

4. Jan 25, 2009

### Staff: Mentor

You want the volume of the balloon, not the total volume.