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### When to use atm or bar

Posted: Wed Nov 18, 2015 1:24 pm
When calculating Kp, does it matter whether we use atm or bar? In the Fall 2014 Quiz 3 Preparation Q8, I understand that the answer should be given in atm since that is the unit provided in the question, but for Q10, is the answer in atm because we use the ideal gas law? Also regarding Q10, why do the significant figures of the answers vary (PH2O=.58 atm --> 2 significant figures) whereas PH2=PCO= 1.47 atm --> 3 significant figures)? Shouldn't both answers use 2 significant figures since the lowest number of significant figures in the question is 2, given by 4.0 L? Thank you in advance!

### Re: When to use atm or bar

Posted: Thu Nov 19, 2015 12:07 am
Doesn't matter which you use as long as you are consistent. The atm and bar differ by only about 1%. In modern times there is an attempt to standardize towards bars, as it is a metric quantity.

### Re: When to use atm or bar

Posted: Wed Nov 25, 2015 10:27 pm
I think the sig figs are given by the initial concentration value of H20 which is has 3 sig figs because the zeroes are trailing the 1 in the decimal making them significant.