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Topic: Calculating Delta E  (Read 8450 times)

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Offline A5HLEY

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Calculating Delta E
« on: January 27, 2008, 02:47:02 PM »
I'm having trouble with a couple of homework problems concerning calculating deltaE.

There are 3 problems, and I got one out of three correct, so I don't know what I'm doing wrong.

a). A system releases 363 kJ of heat to the surroundings and does 2.0e+02 kJ of work on the surroundings;

So I did (-363) - (2e^2) = -377.7781122

and

b). q = 5.62 kJ and w = -495 J

So I converted -495 K to -.495 kJ, and did 5.62 - (-.425) = 6.115


Any ideas as to where I'm going wrong?

Offline Yggdrasil

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Re: Calculating Delta E
« Reply #1 on: January 27, 2008, 03:57:18 PM »
The e notation means scientific notation and does not actually refer to the constant e.

2.0e+02 = 2x102 = 200

For (b) I'm not sure since some people use different conventions for the signs of q and w.  Some people define w as work done on the system in which case ΔE = q + w.  However, if w is defined as work done by the system, then ΔE = q - w.  So, I would check on how w is defined in that particular problem.

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