A house has well-insulated walls. It contains a volume of 100 m3 of air at 300 K. Calculate the energy required to increase the temperature of this diatomic gas by 2oC. Assume it is heating at constant pressure and use Cp=7R/2.

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- Jun 10th 2007, 07:58 AM #1

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- Jun 12th 2007, 05:34 AM #2

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Is R the gas constant? Cp is heat capacity at constant pressure, the energy required to raise the temperature.

Cp=2R/7. R has units J*K^-1*mol^-1, so it must be molar heat capacity we're talking about here.

Consider the ideal gas equation: PV=nRT. You know P, V and T, so you can solve for nR. The energy required will be

Cp*amount of gas [moles]*number of degrees the temperature is raised, so you get the energy E= 4PV/7T

- Jun 12th 2007, 06:22 AM #3
This would be an approximation, but the gas is specifically mentioned to be diatomic, so the ideal gas equation is not correct. We are looking for an equation that relates T and V at constant pressure. As I recall it will involve a ln function, but I don't remember the details.

(I would have answered this question already, but I don't recall the equations and my Thermodynamics book is elsewhere at the moment.)

-Dan