March 28, 2024, 06:59:26 PM
Forum Rules: Read This Before Posting


Topic: Calculate the number of atoms in 21 liters of Helium at 1.15 atms and 0°C  (Read 1146 times)

0 Members and 1 Guest are viewing this topic.

Offline Tgx

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
I know that 1 mole of gas at 0°C and 1 atm has a volume of 22.4 liters. So first, I'll convert the 21 liters of Helium at 1.15 atmospheres to x liters of Helium at 1 atm. For this, I will use the expression:
$$P_{1}V_{1}=P_{2}V_{2}$$
$$1.15*21=1*V_{2}$$
$$V_{2}=24.15$$
So, at 1 atm, we have 24.15 liters of gas. We can use a comparison:
$$\frac{n}{N_{a}}=\frac{24.15}{22.4}$$
Where n is the number of atoms for 24.15 liters of gas and Na is the number of atoms for one mole (22.4 liters) of gas.
$$n=\frac{24.15}{22.4}*N_{a}$$
$$n≈6.49*10^{23}$$

Is this correct? Thank you in advance.

Online Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
OK, but a bit overcomplicated. Just plug the numbers into pV=nRT, find number of moles and you are done.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline billnotgatez

  • Global Moderator
  • Sr. Member
  • ***
  • Posts: 4399
  • Mole Snacks: +223/-62
  • Gender: Male
OK, but a bit overcomplicated. Just plug the numbers into pV=nRT, find number of moles and you are done.

Does that mean that the value for R has to be provided, looked up, or memorized (with proper units).
I guess we can assume the student knows the conversion from kelvin to Celsius.

I do note that the OP has already known
  the relationship of volume and moles at 0 C and 1 atm
  the relationship of moles and  atoms of helium.

Online Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Does that mean that the value for R has to be provided, looked up, or memorized (with proper units).

Yes, but this is one of a few universal constants that are used so often they are worth memorizing (and let's not forget that remembering R is much more universal than remembering volume of 1 mole of gas at STP :) ).
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links