Benzaldehyde, C6H5CHO}, has a normal boiling point of 179.0 C and a critical point at 422 C and 45.9 atm.
Using a phase diagram, estimate its vapor pressure at 125 Degrees
I'm directing it up again to Dr. Bob. (or anyone else who can help)
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If the boiling point (179) is at 1 atm, how would i solve it for 125? Do i subtract the two temperatures? The problem is very vague so I'm still lost
I mentioned the 179 only because it was in the original problem. It has nothing to do with the problem you are trying to solve; I thought it would give you some practice reading the graph. Look at the T axis, find 179, and that point on the P axis should be 1 atm or 760 mm Hg pressure. Now, for the problem, using the same liquid/vapor curve that gave you that number, find 125 on the T axis and read the vapor pressure on the P axis.
That's the problem, I have to make a diagram using only the data made available to me, and I have no idea how to make use of the critical point to solve this. If 179 is indeed equilvalent to 1 atm or 760 mm Hg, i can conclude that at 125 degrees its 0.1-0.9 atm, i just don't kno how to solve it like tihs.
"directing it up again to Dr. Bob".... Why??
To estimate the vapor pressure of benzaldehyde at 125 degrees Celsius, you can utilize the concept of vapor pressure and the given information about its boiling point, critical point, and phase diagram.
First, let's understand the phase diagram. A phase diagram represents the relationship between temperature, pressure, and the state of matter (solid, liquid, or gas) of a substance. The critical point on a phase diagram is the temperature and pressure above which a substance cannot exist as a liquid, regardless of the pressure applied to it. In this case, the critical temperature of benzaldehyde is 422 degrees Celsius, which means it can only exist as gas above this temperature, regardless of pressure.
Now, we need to estimate the vapor pressure at 125 degrees Celsius. Typically, at temperatures below the boiling point, the substance exists as a liquid, and its vapor pressure increases with temperature, approaching but not exceeding the atmospheric pressure. Assuming benzaldehyde behaves similarly, we can estimate its vapor pressure at 125 degrees Celsius.
Since the boiling point of benzaldehyde is given as 179 degrees Celsius at 1 atm pressure, we can assume that at this temperature, the vapor pressure is equal to atmospheric pressure (1 atm). We can use this information to estimate the vapor pressure at 125 degrees Celsius, assuming it's below the boiling point.
To estimate the vapor pressure at 125 degrees Celsius, you can use an empirical approximation known as the Clausius-Clapeyron equation:
ln(P1/P2) = ΔHvap/R * (1/T2 - 1/T1),
where P1 and P2 are the vapor pressures at temperatures T1 and T2 respectively, ΔHvap is the molar enthalpy of vaporization, R is the ideal gas constant (8.314 J/(mol·K)), and T1 and T2 are the corresponding temperatures in Kelvin.
In this case, we are assuming T1 = 179 + 273 = 452 K, P1 = 1 atm, T2 = 125 + 273 = 398 K, and we are solving for P2.
Rearranging the equation to solve for P2:
P2 = P1 * e^(ΔHvap/R * (1/T2 - 1/T1)).
Note that ΔHvap is the molar enthalpy of vaporization, which is the energy required to convert one mole of a substance from liquid to gas at its boiling point (179 degrees Celsius in this case). Unfortunately, the given data doesn't provide this value. You would need to find it in a reference source or use experimental data.
Without the specific value of ΔHvap, it is challenging to provide an accurate estimation of the vapor pressure at 125 degrees Celsius. You may need to consult additional resources or experimental data to obtain the necessary information for a more precise estimation.