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Ideal Gases :

Ideal Gases :. Now that we know how gases behave when we manipulate P, V, and T, it’s time to start thinking about how to deal with things like moles and grams After all, if we’re going to do chemical reactions with gases, we’ll need to know how to calculate these!. Avogadro’s Law.

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Ideal Gases :

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  1. Ideal Gases: • Now that we know how gases behave when we manipulate P, V, and T, it’s time to start thinking about how to deal with things like moles and grams • After all, if we’re going to do chemical reactions with gases, we’ll need to know how to calculate these!

  2. Avogadro’s Law Avogadro’s law:One mole of every gas has the same volume • Gives the relationship between volume and amount when pressure and temperature are held constant • If the amount of gas in a container is increased, the volume increases • If the amount of gas in a container is decreased, the volume decreases • This law assumes that all gases behave perfectly according to the rules of the KMT. Though not precisely true, it gives us very good answers under most conditions

  3. Avogadro’s Law • Avogadro's Law is a direct mathematical relationship. • You prove Avogadro's Law every time you blow up a balloon. • **Remember amount is measured in moles. Also, since volume is one of the variables, that means the container holding the gas is flexible in some way and can expand or contract.

  4. Ideal Gas Behavior • Gaseous particles have very little effect on each other • In fact an ideal gas particle is defined as: • having no volume and no attraction for other particles • Keep in mind this is an ideal, not a real gas • Real gases at room temperature and standard atmospheric pressure (1 atm) can behave nearly ideally since their molecules are so far apart. • When gases are under high pressure and low temperature, their molecules come closer together and no longer act ideally

  5. The Ideal Gas Law • The ideal gas law can be derived from combining two of the gas laws we have already looked at: • The Combined Gas Law & Avogadro’s Law • The Combined Gas Law States: • Where C is a constant which is directly proportional to the amount of gas, n (Avogadro’s Law). The proportionality constant is the universal gas constant, R, i.e. C = nR • Huh you say? Let’s plug in some numbers to see if it really works…

  6. The Ideal Gas Law Cont. • Let’s solve for R using all of the common units we learned about for P, V, T, & n. • PV = R (1.00 atm)*(22.4 L) = R nT (1.00 mol)*(273 K) • What do you get for R? What units? • .08206 atm*L mol * K • What if we used kPa instead of atm? • 8.314 kPa*L mol * K

  7. So how important are writing your units and being in the correct units for all of the Gas Laws? Your answer depends on it!

  8. OK, I know all of the Gas Laws, but which one do I use & when? • Consider: • If “moles” or “grams” are mentioned in the problem, use the ideal gas law (PV = nRT). The other laws don’t use either unit at all • For all other problems, use the combined gas law. NEVER use Boyle’s or Charles’ or Gay-Lussac’s laws! • That’s because you can derive any of the individual gas laws by knowing the combined gas law!

  9. End of: Intro and derivation of the Ideal Gas Law HW for Next Class: Read pgs 426-431, take 5-10 bullet notes AND Complete combined Ideal Gas Law Practice Worksheet (just do the first 5 problems unless you want to get ahead then you can attempt it all)

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