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**MODERATOR'S NOTE: I have been having difficulty explaining to this member the error in his algebraic development, in particular being cavalier in his attentiveness to proper algebraic manipulation of signs. I explained his error in post #7 (and the problems that could arise if he continues to do what he has been doing in more complicated problems), but my message does not seem to be getting through. Any help from the math mavens would be greatly appreciated.**

ChesterMiller

1. Homework Statement

ChesterMiller

1. Homework Statement

Suppose the temperature of an ideal gas decreases from T1 to T2 ( T1>T2). Compare the change in enthalpy and change in internal energy.

## Homework Equations

Change in enthalpy= n * C(p) * delta T

Change in internal energy U = n* C(v) * delta T[/B]

## The Attempt at a Solution

I have almost solved it.

Since temperature is decreasing, we have:

delta H= -n* C(p) * delta T

delta U= -n *C(v)*delta T

C(p) is greater than C(v) , so magnitude wise delta H is greater than delta U. But I am confused with the negative sign. Do I have to compare along with the sign? So in this case, delta U is greater than delta H (which is the correct answer according to my book). I think that the negative sign should not be considered, as it is only showing that the gas does work on the surroundings. Please help me out.

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