Real vs. Ideal Gases(write all of this down)

• - An ideal gas is one who meets all the assumptions of the Kinetic molecular theory..

• However, No gas is truly ideal. • 1. All particles have some volume and there is some

intermolecular attractions. • 2. Despite that, most gases will behave like ideal gases at

many temperatures and pressures.• 3. Ideal Gas Law is not likely to work at extremely high

pressures and low temperatures..• 4. Also polar gases (like water vapor) do not behave ideally

because of the large intermolecular attractions.

Ideal Gas Law

I. The Ideal Gas Law shows the relationship between P, V, T and moles of gas (n)

• A. equation: PV = nRT• 1. where R is the ideal gas constant• R = 0.0821 atm L/mol K (this is a given

value….it never changes). • 2. P= pressure (atm)• 3. V= volume (L)• 3. n= Number of moles (mol)• 4. T = temperature in Kelvin (K)

Example #1• 1. Calculate the number of moles of gas contained in a

3.0 L container at 301 K with a pressure of 1.50 atm• ?- you are solving for n (# of moles)• * If you plug in the numbers given in the problem you

will get:

• (1.50 atm)(3.0L) = n (0.0821 atm L/mol K)(301 K)

• Divide by 0.0821 atm L/mol K) and 301 K to get “n” by itself so your answer is…..

• n = 0.018 mol

Ways that I.G.L can be changed….

• 1. Recall that moles (n) = m/M • (where m = mass and M = molar mass) so

substituting that into the Ideal Gas Law:• PV = mRT• M• 2. Also, recall that density (D) = m/V,

substituting that into the Ideal Gas Law and solving for the density gives:

• D = MP (molar mass X pressure)• RT (I.G. constant x temperature