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A Reminder…

We that we live in an world where: Gas particles have no mass Gas particles have no volume Gas particles have elastic collisions. A Reminder…. assume. ideal. These assumptions are used when trying to calculate the AMOUNT of a gas we have!.

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A Reminder…

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  1. We that we live in an world where: Gas particles have no mass Gas particles have no volume Gas particles have elastic collisions A Reminder… assume ideal These assumptions are used when trying to calculate the AMOUNT of a gas we have!

  2. Why are these assumptions important? PV = nRT Image source: thefreedictionary.com

  3. P V n R T PV = nRT The Ideal Gas Law RESSURE OLUME MOLES OF GAS GAS CONSTANT EMPERATURE Image source: popartuk.com

  4. 8.31 kPa · L 0.0821 atm · L mol · K mol · K 62.4 mmHg · L mol · K The MysteRious R • R is a constant (doesn’t change). • Number value of R depends on other units. • Units of R are a combination of many units. Image source: toysrusemail.com

  5. Ummm… What? PV = nRT Solve for R: P V R = n T Plug in units: (mm Hg) (L) (kPa) (atm) R = (mol) (K)

  6. V1 V2 = T1 T2 P1 V1 P2 V2 = T1 T2 Gas Laws, Gas Laws Everywhere! Charles' Law Boyle's Law P1 x V1 = P2 x V2 Combined Gas Law Ideal Gas Law Used with CHANGING CONDITIONS P V = n R T Used with only ONE SET OF CONDITIONS

  7. When to Use PV = nRT • Calculating amount of gas in moles • Calculating P, V, or T if moles of gas are known. • IMPORTANT! We must have 3 out of 4 pieces of information: • P • V • n • T

  8. Practice with the Ideal Gas Law • A gas sample occupies 2.62 L at 285ºC and 3.42 atm. How many moles are present in this sample?

  9. What Else Happens Under Unchanging Conditions? At constant V and T, pressure is easy to calculate! “The sum of the individual pressures is equal to the total pressure.” Total Pressure = Pressure of gas 1 + Pressure of gas 2 + Pressure of gas 3 + Pressure of gas 4 … Ptotal = P1 + P2 + P3 + … Dalton's Law of Partial Pressures

  10. Partial Pressures Practice A sample of hydrogen gas is collected over water at 25ºC. The vapor pressure of water at 25ºC is 23.8 mmHg. If the total pressure is 523.8 mmHg, what is the partial pressure of the hydrogen? Source: 2003 EOC Chemistry Exam

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