Calculate Sphere Volume: P, T, Radius

[eldon]

how do I calculate the volume of air in a sphere if I know
P, T, radius

 

[cepheid]

When you say in a sphere, do you mean "in a spherical container?" This is the only thing that makes sense to me. If so, then the gas will fill the container, and all you need to know is the volume of the sphere. For that, all you need to know is the radius.

 

[eldon]

its not a rigid tank it is rubber and can stretch

 

[cepheid]

In that case, couldn't you just use the ideal gas law?

 

[eldon]

yea but how does the radius figure in

 

[eldon]

air volume in a balloon

How do I figure out the volume of air in a balloon if I know the radius of the balloon, the air temp, and the pressure?

 

[Doc Al]

If it's a sphere, all you need is the radius to compute the volume.

 

[haiha]

You know the geometric volume of the balloon. You know the pressure, the temp. Apply the real gas law formula:

P1V1/T1 = PoVo/To

 

[eldon]

so the volume of the sphere using 4/3*pi*r^3 would be the same as the volume of the air?

 

[eldon]

how does that relate to the radius of the balloon?

 

[Doc Al]

so the volume of the sphere using 4/3*pi*r^3 would be the same as the volume of the air?

Sure. Simple as that.

 

[cepheid]

In that case, couldn't you just use the ideal gas law?

yea but how does the radius figure in

Maybe this is clear by now, based on other people's responses, but if you know P and T, then the radius is predetermined. It is not an independent variable. The reason is that for an ideal gas, P and T uniquely determine V, which in turn contrains the radius, since the volume is a sphere.