# You have a balloon filled with air. It has a volume of 5.20 gallons at 28.5'C and 745 torr. What volume, in gallons, would the balloon have at –25'C and 250 torr?

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For a given number of moles of a gas (or gas mixture), it follows from the gas laws that,

`(PV)/T` = constant

In other words, `(P_1V_1)/T_1 = (P_2V_2)/T_2` ----- (i)

Here, assuming the gas mixture inside the balloon behaving ideally, `P_1` = 745 Torr.

`V_1` = 5.20 gallons

`T_1` = (273+28.5) = 301.5 K

`P_2` = 250 Torr.

`T_2` = (273-25) = 248 K

`V_2` has to be found out.

Putting the values in equation (i), we get

`(745*5.20)/301.5 = (250*V_2)/248`

`rArr V_2 = (745*5.20*248)/(250*301.5)`

= `12.7463` gallons

= `12.75` gallons (approximately).

**Therefore, the balloon would have a volume of 12.75 gallons at -25****°C and 250 Torr**.

**Sources:**