Recent content by apb000

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    Undergrad Derivative with respect to n of an integral of n(w) over w

    I can't seem to find this anywhere. What's d/dn(∫ n(w) dw)? That's the derivative wrt n of the integral of n over w (note: n is a function of w). Seems straightforward enough. Is there a simplification? Thanks
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    Undergrad Change in pressure and Internal Energy

    I believe that is correct for a monatomic ideal gas. 900 J of heat flows into the system, which raises the temperature, which increases the pressure, which accounts for the increase in internal energy by the relation ΔU=3/2 ΔP V as you say.
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    Graduate Why is ΔH zero for isothermal expansion if heat enters at constant pressure?

    Okay, I think the issue is that I'm imagining the expansion is against a constant pressure, which is perfectly reasonably physically, but the pressure in the gas will not be constant. So I can't take the enthalpy to be equal to the heat flow. Simply, ΔH ≠qP in this situation, and ΔH = 0 even...
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    Graduate Why is ΔH zero for isothermal expansion if heat enters at constant pressure?

    That sounds like it might be the right track to me. Can I get a slightly longer version? I'm taking the system to be just the gas, which I am free to do, and the above reasoning still applies. It sounds like you're saying the solution is that ΔH=0 for an isothermal expansion ONLY if the system...
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    Undergrad Calculating Velocity After Impact: What Went Wrong?

    You need to clarify the question, in particular the line after "but if i do the calculations:" is not clear. Try writing the equation you're using in its general form (using letters) then in the line directly under it, repeat the equation with the specific numbers filled in, and use units. It...
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    Graduate Why is ΔH zero for isothermal expansion if heat enters at constant pressure?

    This is probably a trivial problem, but I can't get it straight. It's well known and easy enough to show mathematically that the change in enthalpy for the reversible isothermal expansion of an ideal gas is always zero, ΔH=0. But it's also true that the enthalpy change for a process at constant...