1. West Valley High School General Chemistry Mr. Mata
Chapter 11B Gases
West Valley High School
General Chemistry
Mr. Mata

2. Standard 4e
Students will know how to calculate gas laws using pressure, temperature, volume, and number of moles.

3. Essential Question
How are the Combined gas law and Ideal gas law used to relate pressure, volume, temperature, and number of moles?

4. S.C.U.B.A. diving in Catalina
What does S.C.U.B.A. stand for???
Self Contained Underwater Breathing Apparatus
Where is Mr. Mata in the photo above???

5. Standard Temperature & Pressure
standard conditions = Reference conditions for gases.
Standard Temp = 273 K or 0oC.
Standard Press =1atm = 760 mm Hg
Together 273 K and 1 atm is called:
Standard Temperature and Pressure (STP)

6. Combined Gas Law
Boyle’s Law & Charles’ Law may be combined into one formula, the Combined Gas Law:
P1V1 = P2V2
T T2
Relates pressure, volume & temperature.

7. Problem #1
A Helium balloon has a volume of 3.0 L at 1 atm and 273 K. Calculate its volume at 2 atm and 27oC.
V1 = 3 L V2 = ?
P1 = 1 atm
T1 = 273 K
P2 = 2 atm
T2 = = 300K

8. Problem #1 (cont’d) T1 T2 V2 = P1V1T2 T1P2 V2 = (1 atm)(3 L)(300 K)
P1V1 = P2V2
T T2
V2 = P1V1T2
T1P2
V2 = (1 atm)(3 L)(300 K)
(273 K )(2 atm)
V2 = 1.7 L

9. Problem #2
A hydrogen balloon has a temperature of 320 K and a volume of 7.5 L and 3 atm of pressure. Calculate its pressure at 58 C and 10.5 L.
V1 = 7.5 L V2 = 10.5 L
P1 = 3 atm
T1 = 320 K
P2 = ?
T2 = = 331 K

10. Problem #2 (cont’d) T1 T2 P2 = P1V1T2 T1V2 P2 = (3 atm)(7.5 L)(331 K)
P1V1 = P2V2
T T2
P2 = P1V1T2
T1V2
P2 = (3 atm)(7.5 L)(331 K)
(320 K )(10.5 L)
P2 = 2.2 atm

11. Standard Molar Volume
The volume of 1 mole of any gas at STP is 22.4 L.
This is called the standard molar volume.
The volume of any gas at STP can be calculated if the number of moles is known:
V = (moles) x 22.4 L

12. IDEAL GAS LAW PV = nRT P = PRESSURE (in atm) V= VOLUME (in L)
n = MOLES OF GAS
R= GAS CONSTANT, L* atm/mol * K
T= TEMPERATURE (in K)
Be consistent with units!

13. Problem #1
Calculate the temp of 7.5 g H2 gas if the volume is 52.5 L and pressure is 0.8 atm.
First convert values to proper units:
n = 7.5 g H2 x 1 mol H2 = 3.8 mol H2
2 g H2
T = ? V = 52.5 L
P = 0.8 atm R = L atm / mol K

14. Problem #1 (cont’d) PV = nRT T = PV nR T= (0.8 atm)(52.5 L)
(3.8 mol)(.0821 L atm/ mol K)
T= K

15. Problem #2
Calculate the pressure of 60 g NH3 gas if the volume is 40 L and temp is 72 C.
First convert values to proper units:
n = 60 g NH3 x 1 mol NH3 = 3.5 mol NH3
17 g NH3
T = 72 C = 345 K V = 40 L
P = ? R = L atm / mol K

16. Problem #2 (cont’d) PV =nRT P = nRT V
P= (3.5 mol)(.0821 L atm/ mol K)(345 K)
(40 L)
P= 2.5 atm

17. Conversion Formulas
K = C + 273
760 torr = 1 atm = 760 mm Hg

18. Chapter 11B SUTW Prompt
Describe how the Combined gas law & Ideal gas law relate pressure, volume, temperature, and moles.
Complete an sentence paragraph using the SUTW paragraph format. Hilight using green, yellow, and pink.
Due Date: Tomorrow (start of class).