Question

A certain volume of a gas had a pressure of 800 torr at a temperature of -40 degrees C. What was the original volume if the volume at STP is now 450.0 cm^3?

(the correct answer is 365 cm^3. I just need an explanation.)

Answer 1

Answer : The original volume of gas is
`365cm^3`

Explanation :

Combined gas law is the combination of Boyle's law, Charles's law and Gay-Lussac's law.

The combined gas equation is,

`(P_1V_1)/(T_1)=(P_2V_2)/(T_2)`

where,

`P_1` = initial pressure of gas = 800 torr

`P_2` = final pressure of gas at STP = 760 torr

`V_1` = initial volume of gas = ?

`V_2` = final volume of gas at STP =
`450.0cm^3`

`T_1` = initial temperature of gas =
`-40^oC=273+(-40) =233K`

`T_2` = final temperature of gas at STP =
`0^oC=273+0=273K`

Now put all the given values in the above equation, we get:

`(800torr* V_1)/(233K)=(760torr* 450.0cm^3)/(273K)`

`V_1= 364.8cm^3\approx 365cm^3`

Therefore, the original volume of gas is
`365cm^3`