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

2. Why are these assumptions important?
PV = nRT
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3. PV = nRT P V n R T The Ideal Gas Law RESSURE OLUME MOLES OF GAS
GAS CONSTANT
EMPERATURE
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4. The MysteRious R 62.4 mmHg · L mol · K 8.31 kPa · L mol · K
R is a constant (doesn’t change).
Number value of R depends on other units.
Units of R are a combination of many units.
62.4 mmHg · L
mol · K
8.31 kPa · L
mol · K
atm · L
mol · K
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5. Ummm… What? PV = nRT P V R = n T (kPa) (mm Hg) (L) (atm) R = (mol) (K)
Solve for R:
P V
R =
n T
Plug in units:
(kPa)
(mm Hg) (L)
(atm)
R =
(mol) (K)

6. Gas Laws, Gas Laws Everywhere!T1 = V2 T2
Charles' Law
Boyle's Law
P1 x V1 = P2 x V2
P1 V1
P2 V2 = T1 T2
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. But Let’s Be Practical…
We don’t usually measure in moles!
We usually measure quantities in GRAMS!
PV = nRT
PVM = gRT

10. PVM = gRT P V M g R T RESSURE OLUME OLAR MASS OF GAS (g/mol)
RAMS OF GAS
GAS CONSTANT
EMPERATURE
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11. Practice with the Ideal Gas Law
A balloon is filled with g of helium to a pressure of 1.26 atm. If the desired volume of the balloon is L, what must the temperature be in ºC?

12. PV=nRT vs. PVM=gRT Use PV=nRT when: Use PVM=gRT when:
You are given moles in the problem.
You are searching for moles as an answer.
Use PVM=gRT when:
You are given grams in the problem.
You are searching for grams as an answer.