At this point ron is slightly confused, this isn’t surprising. however, hermione is doing rather well with them. this also isn’t surprising since she studies every day, as should all students. she feels she can him understand these problems by working with him though another: a 1.00 l sample of dry air contains 0.0319 mol n2, 0.00856 mol o2, and 0.000381 mol ar. if temperature is 25.0◦c what is the partial pressure of n2? express your answer in atmospheres.

The partial pressure of N2 is 0.78 atm.

The following are information contained in the question;

Volume (V) =  1.00 L

Total number of moles of the gases(n) = Number of moles of N2 + Number of moles of O2 + Nuber of moles of Ar = 0.0319 mol + 0.00856 mol + 0.000381 mol = 0.041 moles

Temperature(T) = 25.0◦C + 273 = 298 K

Using PV = nRT

Where;

P = pressure of the gas (the unknown)

V = volume of the sample = 1.00 L

T = absolute temperature = 298K

R = molar gas constant = 0.082 atmLK-1Mol-1

n = total number of moles present = 0.041 moles

Making P the subject of the formula and substituting values;

P = nRT/V

P =  0.041 moles × 0.082 atmLK-1Mol-1  × 298 K/1.00 L

P = 1 atm

Recall that partial pressure = mole fraction × total pressure

Mole fraction of N2 = 0.00856 mol /0.00856 mol  + 0.0319 mol + 0.000381 mol =

Partial pressure of N2 =0.0319 mol /0.041 moles ×  1 atm

Partial pressure of N2 = 0.78 atm

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Explanation:

Hermione is pretty smart. She realizes that, according to Dalton's Law of Partial Pressures, each gas exerts its pressure independently of the others, as if the others weren't even there.

She shows Ron how to use the Ideal Gas Law to solve the problem.

pV = nRT

She collects the data:

V = 1.00 L; n = 0.0319 mol; T = 25.0 °C

She reminds him to convert the temperature to kelvins

T = (25.0 +273.15) K = 298.15 K

Then she shows him how to do the calculation.

Isn't she smart?