Posted by Z on Tuesday, January 20, 2009 at 11:10pm.
i don't get this ?.......If the weather forecast stated that the pressure is 104.2kpa. then what is the pressure in the atmosphere? and what would a barometer measure in mm of mercury
need help please

Chem  DrBob222, Tuesday, January 20, 2009 at 11:14pm
101.325 kPa = 1 atmosphere = 760 mm Hg.
It's just a conversion. 
Chem  Z, Tuesday, January 20, 2009 at 11:18pm
so for the first anwser it would be 101.325kpa because that is the measurement of 1 atmosphere

Chem  DrBob222, Tuesday, January 20, 2009 at 11:42pm
No, of course not. You haven't converted anything. The problem states that the pressure is 104.2 kPa so to convert to atmospheres, we would have
104.2 kPa x (1 atm/101.325) = ?? atm. Notice how the units kPa in the numerator cancel with the kPa in the denominator. The unit atm doesn't cancel with anything which makes the unit of the answer atm which is what you wanted; i.e., pressure in atm. Now you do the one with mm Hg. 1 atm = 760 mm Hg.