Changing molar mass at diff temp and pressures - help

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SUMMARY

The discussion centers on the misconception regarding the relationship between molar mass and changes in temperature and pressure. Molar mass, defined as the mass of one mole of a substance, remains constant regardless of external conditions such as temperature and pressure. The confusion arises from the fact that while the volume of a gas may change under different pressures, the mass and thus the molar mass of the gas does not change. This is a fundamental principle in chemistry that is crucial for accurate lab evaluations.

PREREQUISITES
  • Understanding of the Ideal Gas Law
  • Knowledge of molar mass and its definition
  • Familiarity with standard temperature and pressure (STP) conditions
  • Basic concepts of gas behavior under varying pressure and temperature
NEXT STEPS
  • Study the Ideal Gas Law and its applications in real-world scenarios
  • Review the concept of molar mass and its calculation
  • Explore the effects of temperature and pressure on gas volume
  • Investigate the principles of thermodynamics related to gas behavior
USEFUL FOR

Chemistry students, lab technicians, and anyone involved in gas-related experiments or evaluations will benefit from this discussion.

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 dependent 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 [itex]N_{A}\simeq 6.023\cdot 10^{23} atoms/molecules[/itex].This mass (essentially the mass of the atoms/molecules) is constant with temperature & pressure,if u neglect

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


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

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