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Topic: Expansion coefficient math  (Read 3837 times)

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Offline orgo814

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Expansion coefficient math
« on: August 07, 2013, 09:52:16 AM »
For finding an expansion coefficient I had an expression and evaluated δV/δT at 320 K to get the expression 3.9 x 10^-4/K + 2.96 x 10^-6 x 320/K. The answer is supposedly 1.34 x 10^-3/K and I'm obviously making some sort of math mistake because I'm not getting the answer when I evaluate that expression. I'm sure it's a simple math procedure but if someone could look at that equation and tell me how to get that answer that would be great. This is more a math question than a chemistry question!

Offline Dan

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Re: Expansion coefficient math
« Reply #1 on: August 07, 2013, 10:17:42 AM »
I'm obviously making some sort of math mistake because I'm not getting the answer when I evaluate that expression.

Please show what you are doing, it is a forum rule.
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Offline orgo814

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Re: Expansion coefficient math
« Reply #2 on: August 07, 2013, 10:22:19 AM »
Well that's what I did.. I did the derivatives and got that expression beforehand. I tried solving the expression I gave you and couldn't figure out how they got that exact answer. I tried using order of operations which didn't give me it. I tried factoring out 1/K and didn't get it, etc. that was my reasoning.

Offline orgo814

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Re: Expansion coefficient math
« Reply #3 on: August 07, 2013, 11:01:19 AM »
Disregard my question. Turns out my calculator was misfunctioning!

Offline curiouscat

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Re: Expansion coefficient math
« Reply #4 on: August 07, 2013, 11:03:10 AM »
Disregard my question. Turns out my calculator was misfunctioning!

That's almost in league with "The dog ate my homework"  ;D

...out of curiosity, what calculator do you use?

The closest I remember to this is that one old Intel chip that had a floating point bug.

Offline orgo814

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Re: Expansion coefficient math
« Reply #5 on: August 07, 2013, 11:12:48 AM »
I had a ti 83 but I checked it with a ti 84 and got the answer I was supposed to get so in not sure what's wrong with my previous calculator or if its on some weird setting

Offline curiouscat

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Re: Expansion coefficient math
« Reply #6 on: August 07, 2013, 11:17:40 AM »
I had a ti 83 but I checked it with a ti 84 and got the answer I was supposed to get so in not sure what's wrong with my previous calculator or if its on some weird setting

Probably you misinterpreting a syntax feature. Calculators can be idiosyncratic regarding parenthesis, binding order etc.

Offline Enthalpy

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Re: Expansion coefficient math
« Reply #7 on: August 08, 2013, 02:16:49 PM »
I've had two pocket calculators (over 10) that did a mistake occasionnally. Using them hours a day for years, I finally knew under what computations sequences and values not to trust them. So it does exist - but is uncommon.

I also had one calculator that erased its user-tipped programmes and constants twice a year, but I couldn't determine under what conditions. For sure not my input.

Meanwhile I use a computer with Calcoo, which understands Polish notation and keyboard shortcuts.
Presently in Java, alas (but I still have an old one for Win):
http://calcoo.sourceforge.net/

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