Gases Online Lecture Part 3

Kinetic Molecular Theory Four Postulates 1.The particles are ________ in comparison to the space they occupy that the _______of the individual particles is _________ (zero). 2. Particles are in ______________, the _________ with the walls of the container creates the ________. 3. Particles do not ____________. No ________ or ________. No forces exerted on each other. 4. Kinetic energy (__________________) is ___________ proportional to the T K. This model is for ______ gases, ______ gases do not follow this model!

Can you explain how KMT accounts for the properties of gases by looking at individual gas laws? For example – Boyle’s Law – Why is there an indirect relationship between volume and pressure? Answer: Now try Charles, Avogadro’s and the relationship between Pressure and Temperature. On a separate sheet of paper, ready to turn in tomorrow.

What does temperature measure? The Kelvin temperature is an index of the ______ ______________ of the particles of a gas _________ temperature = __________ motion 3 RT = (KE) average R=8.3145J/Kmol 2 Calculate the KE ave of CH 273 K and 546K.

What can we deduce about KE from this example? Answer on separate sheet of paper to turn in tomorrow.

Root Mean Square Velocity The square root of the average of the square of the individual velocities of gas particles. Big derivation on page 217, you really only need to be able to use the following formula Different R = J/K mol, ( the regular converted to J to give a velocity unit of m/s) M = kg/mol rms = √3RT M

Root Mean Square Velocity Factors that affect velocity of gas particles 1.Collisions____________________________________ ___________________________ 2.Temperature – ____________________________ ________________________________________ Calculate the rms of 25°C. Calculate the rms of O 25°C.

What can you deduce about vrms from these examples? Answer of a separate sheet of paper and turn in tomorrow.

Diffusion vs Effusion Describes _______ of gases (_____________________) Rate of _________ = rate of _________ of gases Very difficult to explain theoretically b/c of the interactions of the individual gases being mixed with air that is already present Describes the _______ _____________________ Rate of ________ = _____________________ _________________ Rate of effusion is ________ proportional to molar mass

More about effusion Graham’s Law of Effusion Rate of effusion for gas 1 = √M2 Rate of effusion for gas 2 √M1 Must have constant temperature and pressure ***Can be used to solve for the unknown molar mass which allows for identification*** Ex. Compare the rates of effusion for H 2 and UF 6.

Without doing any math which gas do you think would effuse faster CO 2 or N 2 ? Answer on your separate sheet of paper and turn in tomorrow.

Ideal Gases vs.Real Gases Most real gases approach ideal pressure and ________ temperature (WHY?) Assumes _____ volume of gas particles when compared to volume of the sample Assumes _____ interaction among particles Gas atoms/molecules do have ________________ Gas particles do _________ with each other, which causes lots of _________, which changes the ________. (this effect is increased by an increase in concentration) Van der Waal’s Equations allows for corrections of pressure and volume in the PV = nRT equation to accurately describe real gases.

Van der Waal’s Corrections Volume - b corrects for volume b/c gas particles do have a ________ volume which changes the _________ volume b/c the gas particles take up some of the space of the container. V – nb is how V should really be described in the equation n = mol, b = empirical constant Interactions – a there are attractive play between gas particles (Van der Waals forces) ______________ __________________________ the size of the correction depends on the concentration of gas particles (__________________________) Pobs = P’ – a (n/v)2 a = proportionality constant n = moles V = volume a and b will be given in a table based on the gas, they are experimentally determined

Van der Waal’s Equations