Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Big-Daddy on November 08, 2013, 06:30:10 PM
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The densities of air at -85°C, 0°C and 100°C are 1.877, 1.294 and 0.946 gdm-3 respectively. Assuming that air obeys Charles' law, determine a value for the absolute zero of temperature in °C.
I know Charles' law - basically the ideal gas equation for a single gas, except that pressure is considered constant to find the volume/temperature ratio - but how does it apply to this question?
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A real crude approximation would be that at absolute zero, the gas has essentially no volume at all.
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Hmm ok, I'm not sure how to use that fact though (which I take note relies heavily on the pressure remaining constant with temperature ...). I did find a completely different way of solving this problem that didn't require setting any V to 0 but I have a feeling you are on the (/a) right track here, can you explain?
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@Big-Daddy
This is a real interesting problem to me.
Will you eventually be getting the expected answer from whence you got the question.
regards
Bill
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Hmm ok, I'm not sure how to use that fact though (which I take note relies heavily on the pressure remaining constant with temperature ...). I did find a completely different way of solving this problem that didn't require setting any V to 0 but I have a feeling you are on the (/a) right track here, can you explain?
First, convert your densities to volumes. Really you can probably just take the inverse, but I used a basis of 1 gram. Plot your volumes as a function of temperature, do a simple linear regression, find the intercept where volume approaches 0. I got a value of about -273.2 °C or something. Closer than I thought it'd be, actually. Neat problem, I have to say.
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The answer is given rather vaguely as -272°C. My answer was -273.32°C average across the data points, but unlike Corribus I did not go as far as linear regression, so you are probably more right.
Thanks for clarifying the method.