1. Basic Gas Laws (Combined and Partial Pressures Laws)
4/27/11

2. Steps for Solving ANY Gas Law Problem:
Write out a column of information down the left-hand side. Make sure all of your variable’s units match (i.e. if P1 is in kPa, then P2 must be in kPa as well). If one doesn’t match, convert it to match the other, using a conversion table. Put a question mark in the space for the variable you are trying to solve for (what you DON’T have).
Write the original equation for the gas law you will be using.
Rearrange the equation to solve for the variable you need.
Plug in the values and units you have in to the rearranged equation, and make sure all your units will cancel except for one. This will be the unit for your answer.
Calculate, then box your answer!

3. millimeters of mercury
Part 5: The Combined Gas Law (1802)
the Combined Gas Law takes Boyle’s, Charles’s, and Gay-Lussac’s Law and combines them into one.
Ex4: A sample of gas took up 35.0L of space at 124C and kPa. If the temperature increased by 16C and the pressure changed to atm, what would the resulting volume be?
Ex5: The volume of a balloon is 3.70L at 15.8C and 1.3 atm pressure. What volume will the balloon have at STP?
Combined Gas Law
P1V1 = P2V2
T T2
Unit
Abbr.
STP value
atmospheres
atm
1 atm
millimeters of mercury
mmHg
760 mmHg
pounds per square inch
psi
14.7 psi
kilopascals
kPa
kPa

4. P1V1T2 = P2V2T1 V2 = P1V1T2 _____ _____ P2T1 P2T1 P2T1
Ex4: A sample of gas took up 35.0L of space at 124C
and kPa. If the temperature increased by 16C
and the pressure changed to 4.56 atm, what would the
resulting volume be?
P1 = __________
V1 = __________
T1 = ____C____K
P2 = __________
V2 = __________
T2 = ____C____K
Combined Gas Law
P1V1 = P2V2
T T2
P1V1T2 = P2V2T1
_____ _____
P2T P2T1
V2 = P1V1T2
P2T1
84.56 kPa
35.0 L
124
4.56 atm ?
140
= atm
397
413
84.56 kPa
1 atm =
0.835 atm
kPa
V2 = (0.835 atm)(35.0 L)(413 K) =
(4.56 atm)(397 K)
V2 = 0.835 35.0  413 ÷ (4.56  397) =
6.67 L

5. V2 = P1V1T2 P2T1 V2 = (1.3 atm)(3.70 L)(273 K) = (1 atm)(288.8 K)
Ex5: The volume of a balloon is 3.70L at 15.8C and
1.3 atm pressure. What volume will the balloon have
at STP?
P1 = __________
V1 = __________
T1 = ___C_____K
P2 = __________
V2 = __________
T2 = ____C____K
Part 6: The Partial Pressures Law (1803)
the Partial Pressures Law states that the total pressure of a mixture of gases equals the sum of the partial pressure of each gas.
partial pressures are written as P[formula of gas]
P1, P2, and P3 represent the partial pressures in the formula
Ex6: A gas mixture contains oxygen, nitrogen, and carbon kPa. If P[O2] = kPa, and P[N2] = 0.25 atm, what is P[CO2] ?
Combined Gas Law
P1V1 = P2V2
T T2
V2 = P1V1T2
P2T1
1.3 atm
3.70 L
15.8
1 atm ?
V2 = (1.3 atm)(3.70 L)(273 K) =
(1 atm)(288.8 K)
288.8
V2 = 1.3  3.70  273 ÷ (1  288.8) =
V2 = 4.55 L
Partial Pressures Law
PT = P1 + P2 + P3

6. PT = P1 + P2 + P3 - P1 - P2 - P1 - P2 P3 = PT - P1 - P2
Ex6: A gas mixture contains oxygen, nitrogen, and
carbon 72.9 kPa. If P[O2] = kPa,
and P[N2] = 0.25 atm, what is P[CO2] ?
PT = __________
P1 = __________
P2 = __________
P3 = __________
Partial Pressures Law
PT = P1 + P2 + P3
72.9 kPa
26.60 kPa
0.25 atm ?
PT = P1 + P2 + P3
- P1 - P P1 - P2
P3 = PT - P1 - P2
= kPa
0.25 atm
kPa =
25.33 kPa
1 atm
P3 = 72.9 kPa – kPa – kPa =
20.97 kPa