Question

Find vapor pressure of the following substances at 10.1 degrees celsius, 25.4 degrees celsius, and 45.6 degrees celsius in mmHg. What is the phase of each substance at room temperature 22.2 degrees celcius. A) Ethanol B)m-Xylene C)Acetone

Answer 1

In order to do this, I need the following data:

for Ethanol, m-Xylene and Acetone

Vapor pressure of each compound at 25 °C (298 K).

With those data, I can easily calculate the vapor pressure at that temperature.

However, let me give you an idea of how you will do it with that data, and the expression you need to use in order to find the vapor pressure. There are two ways to calculate this, one is with Raoult Law, but we don't have enough data (such as mass of each compound and mass of solvents used) to do so. The other way is with the Claussius Clapeyron equation which is:

ln (P2/P1) = /R (1/T1 - 1/T2)

Assume that P2 is the vapor pressure at the temperature given, and P1 is the vapor pressure at 299 K (25°C). With that data, you only need to solve for P2, which would be:

P2/P1 = exp[/R (1/T1 - 1/T2)]

P2 = P1exp[/R (1/T1 - 1/T2)]

Now, I have the vapor pressure of ethanol at 25 °C which is 58.9 Torr (mmHg) and enthalpy of vaporization is 38.6 kJ/mol. So, I will do this with the first temperature given so you can have an idea, but you need to use that missing data in order to find the vapor pressure. Now replacing these values in the equation we have:

P2 = 58.9 exp[38600 J/mol / 8.3144 J/mol K (1/298 - 1/283.1)K]

P2 = 58.9 exp(-0.825743093)

P2 = 25.79 mmHg

Doing this with the other temperatures, and you'll get the vapor pressures at those temperatures in mmHg. Remember to look and use the enthalpy of vaporization and vapor pressures of the other compounds at 25 °C (or 20 °C).

Hope this helps