The vapor pressure of the liquid HF is measured at different temperatures. The following vapor pressure data are obtained.
Temperature(K) Pressure mmHg
250 129.63
260 206.65
270 318.22
280 475.16
Determine the enthalpy of vaporization.
I have know idea how to start this. Thank you for your help.
You are supposed to plot ln p vs 1/T. You will get a straight line with a negative slope. The slope = dHvap/R.
Ok when I did the graph I got -2.99e3 as the slope. Is this the answer or do I have to do something else now?
Nevermind I actually figured it out. Thank you.
well i would really help u hannah if i knew how to do it
To determine the enthalpy of vaporization, you can use the Clausius-Clapeyron equation. This equation relates the vapor pressure of a substance to its temperature and enthalpy of vaporization.
The Clausius-Clapeyron equation is given as:
ln(P2/P1) = (-ΔHvap/R) * (1/T2 - 1/T1)
Where:
P1 and P2 are the initial and final vapor pressures respectively,
T1 and T2 are the initial and final temperatures in Kelvin (K),
ΔHvap is the enthalpy of vaporization in joules (J),
R is the gas constant (8.314 J/(mol·K)).
In your case, you have the vapor pressure data at different temperatures. Let's assume the initial temperature and pressure are 250 K and 129.63 mmHg, respectively. Now we can use the equation to calculate the enthalpy of vaporization.
First, convert the pressures from mmHg to atm (divide by 760):
P1 = 129.63 mmHg / 760 mmHg/atm ≈ 0.1706 atm
P2 = 475.16 mmHg / 760 mmHg/atm ≈ 0.6252 atm
Next, convert the temperatures from Celsius to Kelvin:
T1 = 250 K
T2 = 280 K
Now, substitute the values into the Clausius-Clapeyron equation:
ln(0.6252/0.1706) = (-ΔHvap/8.314) * (1/280 - 1/250)
Calculate the natural logarithm on the left side of the equation using ln (natural logarithm) function on your calculator or computer. Then solve for ΔHvap.
ΔHvap ≈ -[ln(0.6252/0.1706) / (1/280 - 1/250)] * 8.314
This will give you the enthalpy of vaporization in joules, which you can convert to kilojoules (kJ) by dividing by 1000.
Note: Make sure to keep track of significant figures throughout the calculations for accurate results.