Sorry for some many questions here. I'm stuck on all of these problems and it's starting to really frustrate me. I'm not sure what more to do.(adsbygoogle = window.adsbygoogle || []).push({});

1. A sample of Helium behaves as an ideal gas as energy is added by heat at constant pressure from 273 K to 403 K. If the gas does 20.0 J of work, what is the mass of helium present?

>> At first I was going to use Q=mct, but I do not know c of helium and it's not in my physics book. Then I tried to use Q=mL which I think should work, but I don't know how to convert W to Q.

2. A gas is compressed from 10.00 L to 3.00 L at a constant pressure of 0.800 atm. In the process, 330 J of energy leaves the gas by heat. What is the work done by the gas? What is the change in its internal energy?

>> I know trial and error isn't the way to approach physics, but I'm lost. I tried using W=Pln(Vf/Vi) and got an answer of .963 J. I don't understand why this is wrong...

3. A thermal window with an area of 6.00m^2 is constructed of two layers of glass, each 4.00 mm thick and separated from each other by an air space of 4.00 mm. If the inside is at 20.0 C and the outside is at -34.0 C, what is the rate of energy transfer by conduction through the window?

>> I know I need to use the formula H=kA(change in T/L). But... do I have to do this using only the air in the middle of the two panes of glass? Or do I have to do the formula three times: one for the air, and two each piece of glass? And if so, is the change in temperature the same?

4. Gas in a container is at a pressure of 1.40 atm and a volume of 6.00 m^3. What is the work done by the gas if it expands at a constant pressure to twice its initial volume.

>> I think I need to use W=Pln(Vf/Vi). When I did this, though, I got .970... which isn't the answer according to webassign. I honestly don't know why this doesn't work. Does P have to be in a different unit?

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# Homework Help: Thermodynamic Questions

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