I have discovered recently that when we have a balloon in a room filled with air, with temperature $T_1$, and then this balloon gets a hole and air is let out, the temperature of the air that comes out is $T_2$, which is less than $T_1$. However, I was doing a problem recently:

23) An inflated balloon, filled with a gas of temperature $T$, is held in a room with the same temperature. If we make a small hole on the side of the balloon and let the gas escape, which statement is true about the temperature $T’$ of the gas right after leaving the balloon?

a) $T' > T$

b) $T' = T$

c)$ T' < T$

I answered (c), because I thought that it was an adiabatic expansion (work in air is positive when it flies out, thus by $U = Q - \Delta{W} = -\Delta{W}$ the temperature decreases, so the answer should be (c)). However, the apparently correct answer is (a). I think this might be due to the air particles from the balloon colliding with more particles outside the balloon due to their higher average kinetic energy, but I am not sure... Can someone please explain why the answer is (a)?


The balloon's elastic releases its potential energy, increasing the average kinetic energy of air particles, so the temperature increase.

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  • $\begingroup$ This answer may or may not be correct; it uses an unusual grammar which makes it very difficult to understand. $\endgroup$ – rob May 29 '18 at 19:26

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