If you place 1.0 L of ethanol (C2H5OH) in a small laboratory that is 3.0 m long, 2.0 m wide, and 2.0 m high, will all the alcohol evaporate? If some liquid remains, how much will there be? The vapor pressure of ethyl alcohol at 25 °C is 59 mm Hg, and the density of the liquid at this temperature is 0.785g/cm^3 .
will all the alcohol evaporate? or none at all?
Answer:
Yes, all the ethanol present in the laboratory will evaporate since the mole of ethanol present in vapor is greater. The volume of ethanol left will therefore be zero.
Explanation:
Given that:
The volume of alcohol which is placed in a small laboratory = 1.0 L
Vapor pressure of ethyl alcohol at 25 ° C = 59 mmHg
Converting 59 mmHg to atm ; since 1 atm = 760 mmHg;
Then, we have:
= ![\frac{59}{760}atm](https://tex.z-dn.net/?f=%5Cfrac%7B59%7D%7B760%7Datm)
= 0.078 atm
Temperature = 25 ° C
= ( 25 + 273 K)
= 298 K.
Density of the ethanol = 0.785 g/cm³
The volume of laboratory = l × b × h
= 3.0 m × 2.0 m × 2.5 m
= 15 m³
Converting the volume of laboratory to liter;
since 1 m³ = 100 L; Then, we have:
15 × 1000 = 15,000 L
Using ideal gas equation to determine the moles of ethanol in vapor phase; we have:
PV = nRT
Making n the subject of the formula; we have:
![n = \frac{PV}{RT}](https://tex.z-dn.net/?f=n%20%3D%20%5Cfrac%7BPV%7D%7BRT%7D)
![n = \frac{0.078 * 15000}{0.082*290}](https://tex.z-dn.net/?f=n%20%3D%20%5Cfrac%7B0.078%20%2A%2015000%7D%7B0.082%2A290%7D)
n = 47. 88 mol of ethanol
Moles of ethanol in 1.0 L bottle can be calculated as follows:
Since numbers of moles = ![\frac{mass}{molar mass}](https://tex.z-dn.net/?f=%5Cfrac%7Bmass%7D%7Bmolar%20mass%7D)
and mass = density × vollume
Then; we can say ;
number of moles = ![\frac{density*volume }{molar mass of ethanol}](https://tex.z-dn.net/?f=%5Cfrac%7Bdensity%2Avolume%20%7D%7Bmolar%20mass%20of%20ethanol%7D)
number of moles =![\frac{0.785g/cm^3*1000cm^3}{46.07g/mol}](https://tex.z-dn.net/?f=%5Cfrac%7B0.785g%2Fcm%5E3%2A1000cm%5E3%7D%7B46.07g%2Fmol%7D)
number of moles = ![\frac{&85}{46.07}](https://tex.z-dn.net/?f=%5Cfrac%7B%2685%7D%7B46.07%7D)
number of moles = 17.039 mol
Thus , all the ethanol present in the laboratory will evaporate since the mole of ethanol present in vapor is greater. The volume of ethanol left will therefore be zero.