Changing molar mass at diff temp and pressures - help

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The discussion centers on the relationship between the volume, mass, and moles of hydrogen gas under varying pressure conditions. Jon questions whether increasing pressure on a fixed mass of hydrogen gas would affect its molar mass, suggesting that molar mass might depend on environmental conditions. Daniel clarifies that molar mass is a constant value defined as the mass of one mole of a substance, approximately 6.023 x 10^23 atoms or molecules, and remains unchanged with variations in temperature and pressure, barring extreme conditions like nuclear reactions or significant energy changes. This clarification resolves Jon's confusion regarding the dependence of molar mass on external factors.
rocketboy
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Hi,

If I have a 50mL volume of hydrogen gas at standard temperature and pressure, and then increae the pressure, the volume is going to drop. Let's say that I know there is 1.5 grams of hydrogen gas in there. So if the volume drops, the mass of the hydrogen gas stays the same, but the number of moles of hydrogen will change, meaning that the molar mass is going to change. Is this correct? If not where did I go wrong and why?

If I am correct than that means molar mass of a substance is dependant on its surroundings...so are the molar masses in the periodic table at STP?

It's really important I know this for the evaluation of my lab report.
Thanks everybody,
-Jon
 
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You couldn't be any wronger.The molar mass is the mass of 1 mole of substance = the mass of N_{A}\simeq 6.023\cdot 10^{23} atoms/molecules.This mass (essentially the mass of the atoms/molecules) is constant with temperature & pressure,if u neglect

a) Einstein's formula E=mc^{2}
b) Radiation loss /gain of atoms.
c) Nuclear reactions...


Daniel.
 
lol, that makes complete sense now, thanks.
 

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