Wednesday, January 18, 2017

homework - Volume change inside a balloon upon decreasing the the outer pressure




A balloon is filled with hydrogen at room temperature. It will burst if pressure exceeds 0.2 bar. If at 1 bar pressure the gas occupies 2.27 L volume, upto what volume can the balloon be expanded?



Now i can easily figure out that the pressure is 0.2bar at a volume of 11.35L. However, when i check the answer in my book, it says that the volume of the balloon should be less than 11.35L.


However, if you decrease the volume from 11.35L, wouldn't the pressure become greater than 0.2bar, hence bursting the balloon?



Answer



The relationship between pressure and volume is given by Boyle's Law. $$\mathrm{P}_1\mathrm{V}_1 = \mathrm{P}_2\mathrm{V}_2$$


      P       V
0.199 11.41
0.20 11.35

0.201 11.29

1.0 2.27

So yes, you're right. Using Boyle's Law, the volume should be more than 11.35L so the pressure stays below 0.20 bar.




However this doesn't make real world sense. When you blow up a balloon, as the pressure increases the volume increases.


Edit - Thanks @Mithoron here is a version of the problem that works...





A balloon is filled with hydrogen at room temperature (25 C) and pressure (1.00 bar) to a volume of 2.27 L in a chamber. The pressure in the chamber is then reduced isothermally. The balloon will burst when the pressure in the chamber is reduced to 0.200 bar. What will the volume of the balloon be just as it explodes?




No comments:

Post a Comment

periodic trends - Comparing radii in lithium, beryllium, magnesium, aluminium and sodium ions

Apparently the of last four, $\ce{Mg^2+}$ is closest in radius to $\ce{Li+}$. Is this true, and if so, why would a whole larger shell ($\ce{...