[orgo814]

The vapor pressure, P, of nitric acid varies with temperature as follows:
T/Celsius: 0, 20, 40, 50, 70, 80, 90, 100
P/kPa: 1.92, 6.38, 17.7, 27.7, 62.3, 89.3, 124.9, 170.9

What is the normal boiling point? What is the enthalpy of vaporization of nitric acid?

I'm guessing this has to do with the clausius-clapeyron equation: dlnP/dT = delta H/RT^2. Integrated, it's lnP = Constant - delta H/RT
I'm confused how to get that expression though. I'm pretty bad at excel. I'm not even sure if my method is correct. I just know if I get an expression from excel I can solve for the delta H vap and that I can find the normal boiling point too.

Thanks for any insight.

[Corribus]

You've got the right equation, and you can see a linear relationship between what operations of P and T?

[orgo814]

Unsure of what U mean. I expect them to be directly proportional

[Enthalpy]

Clausius-Clapeyron would be the right attempt, but you have to observe the equation better to see the right proportionality. Excel is nothing mandatory here (...Kelvin are, just in case).

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What I wonder, but is probably not meant in the question: pure nitric acid doesn't exist. If it doesn't contain water, it contains varied nitrogen oxides which are more volatile than HNO₃. So I wonder what kind of pressure can be measured, and if said measure makes any sense to the evaporation of nitric acid.

[Corribus]

Unsure of what U mean. I expect them to be directly proportional

Look at your equation. P is not directly proportional to T.

[orgo814]

the greater T increases, the less P increases i'm guessing is the pattern you're trying to get me to see. how would i apply that to the clausius-clapeyron equation though to get the delta H vap and temperature?

[billnotgatez]

just a side note
terminology
http://www.mathsisfun.com/algebra/directly-inversely-proportional.html
Directly Proportional and Inversely Proportional

[Corribus]

the greater T increases, the less P increases i'm guessing is the pattern you're trying to get me to see.

Yes, but if T increases, P doesn't decrease linearly. However, to do a linear fit, you need to plot one variable against another such that the dependence is linear.  In your (integrated) equation, can you see a way to plot T and P, such that the dependence is linear?  That is, can you turn the T and P terms into modified variables, such that the integrated equation takes on a familiar linear equation, y = mx + b?

[orgo814]

Would I plot natural log of P versus T then get linear best fit (y= mx + b). Would b be my delta H/R?

[orgo814]

Or natural log verses 1/T?

[Corribus]

I think you might be on to something now. Sounds like it's time to do a linear regression.