[Retsu Unohana]

Hi all,

I'm wondering if I have my reasoning right for this problem. Say I have 11.5 g of Na (1/2 mol) and it takes 46 kJ of energy to turn it into a gas. At 25 C and 760 mm Hg, what would the volume of the gas be?

I thought that since the gas was slightly above STP that it's volume would be between 11.2 L and 22.4 L. Am I correct?

Thanks

[Borek]

Are you sure about the wording of the question?

[Retsu Unohana]

I'm pretty sure that's how it was worded. Is there anything wrong?

[sjb]

I'm pretty sure that's how it was worded. Is there anything wrong?

What I think Borek was considering was the fact that the 46 kJ of energy clause seems to be extra information that wasn't actually needed to answer the main question.

[Johnny010]

Yes, it would be 11.2. But this is treating Na_(g) as ideal, which it really is not.

Use the Van der Waals equation:

(P+(n²*a/V²))(V-n*b)=nRT

It is quite hard to find the constants a and b for sodium...

[Retsu Unohana]

Yes, this is assuming that it is an ideal gas. I also thought the 46 kJ was extra info, so I didn't figure that into my calculations.

But wouldn't the final answer be slightly larger than 11.2 L because the temperature is 25 C instead of 0 C (STP)?

[Johnny010]

Well: PV=nRT
V=nRT/P

0.5*8.314*298 / 101000   =   0.012265
0.5*8.314*273 / 101000   =   0.011236

It is marginal(about 10%)...but the answer (ideal gas assumed) would be 0.012265m³.

*1000 (to litres):

12.265 litres.

[Borek]

Problem is, sodium is not a gas so close to STP, so calculating its volume doesn't make much physical sense...

[billnotgatez]

I think they ment to put N₂ and not Na