Sig Figs For Thermodynamic Problems?


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Vivien Ho 3L
Posts: 30
Joined: Fri Sep 26, 2014 2:02 pm

Sig Figs For Thermodynamic Problems?

Postby Vivien Ho 3L » Sun Jan 25, 2015 11:48 am

If the question contains a number with two sig figs like 30C, does this mean that all answers have to be 2 sig figs even though "30C" is not used in the question?
For Self Test 7.2B, I got -0.20kJ and -1.7kJ for my answers so they had two sig figs. However, the answers are -202J and and 1.75kJ. Can anyone explain this?

Neil DSilva 1L
Posts: 70
Joined: Fri Sep 26, 2014 2:02 pm

Re: Sig Figs For Thermodynamic Problems?

Postby Neil DSilva 1L » Sun Jan 25, 2015 12:41 pm

If the number isn't used in the calculations, it isn't used in determining sig figs. We round off using sig figs because the measurements obtained are limited to the accuracy of the tools used to obtain them, so our answers can only be accurate for a certain amount of significant digits. If a number isn't used in the calculations, it doesn't affect the accuracy of the answer.

Chem_Mod
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Re: Sig Figs For Thermodynamic Problems?

Postby Chem_Mod » Tue Jan 27, 2015 4:30 pm

Avoid rounding off any intermediate values until you get the final answer.

Then round your final answer off to the significant figures of the least accurate data value. Constants and exact coefficients like "8.314 J/mol K" and "3 moles" don't count since they are not measured quantities.


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