What is the number of moles in 500 L of He gas at STP

2 answers:

6 0

Answer:

20 moles

Explanation:

The important thing to realize here is that you're working under STP conditions, which implies that you can use the molar volume of a gas at STP to find how many moles of helium will occupy that volume.
Now, the molar volume of a gas represents the volume occupied by one mole of a gas under some specific conditions for pressure and temperature.
Starting from the ideal gas law equation

PV=nRT

you can say that the molar volume of gas at a pressure P and a temperature T will be equal to

Vn=RTP

Now, Standard Temperature and Pressureconditions are defined as a pressure of 100 kPaand a temperature of 0∘C. Under these specific conditions, the molar volume of a gas will be equal to

Vn=0.0821⋅atm⋅Lmol⋅K⋅(273.15+0)K100101.325atm
Vn=22.7 L/mol

This of course implies that one mole of any ideal gas will occupy 22.7 L.
In your case, the volume of the gas is said to be equal to 500 L. This means that you will have

500L⋅1 mole He22.7L=22.026 moles He

Rounded to one sig fig, the number of sig figs you have for the volume of the gas, the answer will be

nHe=20 moles

SIDE NOTE Many textbooks and online sources still list STP conditions as a pressure of 1 atmand a temperature of 0∘C.
Under these conditions for pressure and temperature, one mole of any ideal gas occupies 22.4 L. If these are the values for STP given to you by your instructor, make sure to redo the calculations using 22.4 L instead of 22.7 L

sergey [27]3 years ago

5 0

Answer:

22.3 mol

Explanation:

He is in STP conditions

This means that it is in standard conditions of temperature and pressure, under these conditions the pressure has a value of 1 atm and the temperature has a value of 273 K

To calculate the number of moles in 500L of He gas we use the ideal gas equation

$P.V=n.r.T\\r(constant of ideal gases)= 0.082\frac{atm.L}{K.mol}$

We cleared the moles (n)

$P.V=nr.T\\\frac{P.V}{r.T}=n\\\frac{1atm.500L}{0.082atm.L/K.mol.273K}=n\\\\22.3 mol=n$

The number of moles in 500 L of He gas at STP 22.3 mol

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