1. Gases
Physical Properties

2. Kinetic Molecular Theory
Particles in an ideal gas…
have no volume. The particles in a gas are very far apart.
have elastic collisions.
are in constant, random, straight-line motion.
don’t attract or repel each other.
have an avg. KE directly related to Kelvin temperature.

3. Real Gases Particles in a REAL gas… have their own volume
attract each other
Gas behavior is most ideal…
at low pressures
at high temperatures

4. Characteristics of Gases
Gases expand to fill any container.
Gases have very low densities.
no volume = lots of empty space
Gases can be compressed
Compressibility—a measure of how much the volume of matter decreases under pressure

5. Characteristics of Gases
Gases undergo diffusion & effusion.
Diffusion –the tendency of molecules to go from areas of high concentration to area of low concentration
Effusion – the process when a gas escapes through a tiny hole in a container

6. Temperature
Always use the Kelvin scale when working with gases. ºF ºC K
-459 32
212
-273
100
273
373
K = ºC + 273

7. Pressure
Which shoes create the most pressure?

8. Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm
760 mm Hg
760 torr
14.7 psi

9. Standard Temperature & Pressure
STP
STP
Standard Temperature & Pressure
0°C K
1 atm kPa
-OR-

10. Temperature Conversions
Convert each of the following to Kelvin temperatures
27 °C
-50 °C
-273 °C

11. Answers
300 K
223 K
0 K

12. Temperature Conversions
Convert each of the following to degrees Celsius
273 K
350. K
100. K
20. K

13. Answers
0 °C
77 °C
-173 °C
-253 °C

14. Pressure Conversions Convert 109 kPa to atm Convert 0.62 atm to mm Hg
Convert atm to kPa
Convert mmHg to kPa

15. Answers
1.08 atm
470 mm Hg
kPa
3.91 kPa

16. Gases
The Gas Laws P V T

17. Boyle’s Law The pressure and volume of a gas are inversely related
at constant mass & temp P V

18. Charles’ Law
The volume and absolute temperature (K) of a gas are directly related
at constant mass & pressure V T

19. Gay-Lussac’s Law
The pressure and absolute temperature (K) of a gas are directly related
at constant mass & volume P T

20. Combined Gas Law
P1V1 T1 =
P2V2 T2
P1V1T2 = P2V2T1

21. Gas Law Problems
A gas occupies 473 cm3 at 36°C. Find its volume at 94°C.
GIVEN:
V1 = 473 cm3
T1 = 36°C = 309K
V2 = ?
T2 = 94°C = 367K T V
WORK:
P1V1T2 = P2V2T1
(473 cm3)(367 K)=V2(309 K)
V2 = 562 cm3

22. Gas Law Problems
A gas occupies 100. mL at kPa. Find its volume at 200. kPa.
GIVEN:
V1 = 100. mL
P1 = 150. kPa
V2 = ?
P2 = 200. kPa P V
WORK:
P1V1T2 = P2V2T1
(150.kPa)(100.mL)=(200.kPa)V2
V2 = 75.0 mL

23. Gas Law Problems P T V V1 = 7.84 cm3 P1 = 71.8 kPa
A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its volume at STP.
GIVEN:
V1 = 7.84 cm3
P1 = 71.8 kPa
T1 = 25°C = 298 K
V2 = ?
P2 = kPa
T2 = 273 K
P T V
WORK:
P1V1T2 = P2V2T1
(71.8 kPa)(7.84 cm3)(273 K)
=( kPa) V2 (298 K)
V2 = 5.09 cm3

24. Gas Law Problems
A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr?
GIVEN:
P1 = 765 torr
T1 = 23°C = 296K
P2 = 560. torr
T2 = ? P T
WORK:
P1V1T2 = P2V2T1
(765 torr)T2 = (560. torr)(296K)
T2 = 217 K = -56°C