### Sig Figs

Posted:

**Tue Feb 14, 2017 11:02 pm**When the problem says "at 25 degrees celsius," do we take that constant into account when doing sig figs?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=161&t=19536

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Posted: **Tue Feb 14, 2017 11:02 pm**

When the problem says "at 25 degrees celsius," do we take that constant into account when doing sig figs?

Posted: **Wed Feb 15, 2017 12:13 am**

I think the answer to this is that it depends. Sometimes you will be given the temperature just so that you know that some given values are valid. For example, the standard enthalpies of formation are usually given at 25 degrees C, so often the only reason you are given the temp is so that you know that those enthalpy values apply to the problem at hand. However if you are using the temperature as a part of your calculations then it does need to be taken into account when evaluating the number of significant figures. So if you use the temperature value in your calculations then its sig figs must be taken into account, but if not then they do not.

Posted: **Fri Feb 17, 2017 10:24 am**

In general, sig figs apply only within the numbers you use for your calculations.

Posted: **Sun Feb 19, 2017 1:34 pm**

Does this mean that we only use sig figs at the end of each problem, such as say, we are given numbers in the problem with only 3 sigfigs, so do we end the problem with 3 too and disregard the addition/multiplication etc that the problem requires?

Posted: **Sun Feb 19, 2017 2:50 pm**

It is important to keep track of the number of sig figs throughout the problem, but I usually save rounding off numbers used in calculations until the end for more precision. You need to be careful with addition/subtraction vs. multiplication/division because they have different rules when determining sig figs, so I wouldn't dismiss sig figs until the end. A trick I normally use is that throughout the problem (after a calculation), I write my calculated number rounded to sig figs and my unrounded calculated number to the side, that way I can keep track of sig figs, but still use the precise numbers for further calculations. Hope this helps!

Posted: **Sun Feb 19, 2017 4:37 pm**

If given a question where it says to calculate something such as the standard enthalpies of formation then you would not use the 25 degrees celsius value in determining the number of sig figs. However, if the problem has to do with calculating something that is not at standard conditions then I believe you must take into account the temperature into the number of sig figs.