04-12-2018, 03:38 AM

Hi,

I'm preparing for a Chem practical (gases) in which we are using a vacuum line hooked to a manometer to determine the delta H_v (latent heat of vaporisation) of n-pentane. Basically, we have a sample of pentane in vacuum, which is thawed from solid into liquid. This pentane then goes into equilibrium with its vapour. By changing the temperature of the system, the vapour pressure changes. We then plug the (P, T) data into integrated Clausius-Clapeyron equation to get a linear graph of ln(p) vs. 1/T, and hence calculate its gradient and delta H_v.

There is one discussion question which I am confused with, and one of the lab demonstrators isn't too sure about it either - we are told "do not take the temperature [of the system] above room temperature". The demonstrator told me that, above room temperature, the data would not be linear... but wasn't sure why.

Hence I'm asking here. Given that I've posted the essence of the experiment above, are there any reasons for why we shouldn't take the temp above room temp?

Thanks,

I'm preparing for a Chem practical (gases) in which we are using a vacuum line hooked to a manometer to determine the delta H_v (latent heat of vaporisation) of n-pentane. Basically, we have a sample of pentane in vacuum, which is thawed from solid into liquid. This pentane then goes into equilibrium with its vapour. By changing the temperature of the system, the vapour pressure changes. We then plug the (P, T) data into integrated Clausius-Clapeyron equation to get a linear graph of ln(p) vs. 1/T, and hence calculate its gradient and delta H_v.

There is one discussion question which I am confused with, and one of the lab demonstrators isn't too sure about it either - we are told "do not take the temperature [of the system] above room temperature". The demonstrator told me that, above room temperature, the data would not be linear... but wasn't sure why.

Hence I'm asking here. Given that I've posted the essence of the experiment above, are there any reasons for why we shouldn't take the temp above room temp?

Thanks,