1. Properties of Gases
Gas Pressure

2. Gases A gas consists of small particles that:
move rapidly in straight lines.
have essentially no attractive (or repulsive) forces.
are very far apart.
have very small volumes compared to the volume of the container they occupy.
have kinetic energies that increase with an increase in temperature.

3. Gases
Gases are described in terms of four properties: pressure (P), volume (V), temperature (T), and amount (n).

4. Gas Pressure Gas pressure is a force acting on a specific area.
Pressure (P) = force
area
has units of atm, mmHg, torr, and kilopascals(kPa).
1 atm = mm Hg (exact)
1 atm = 760 torr
1 atm = Pa
1 atm = kPa
1 kPa = mm Hg

5. Here is how you convert units
2.5 atm = _______ mmHg
2.5 atm x 760 mm Hg =
1 atm

6. Here is how you convert units
2.5 atm = _______ mmHg
2.5 atm x 760 mm Hg = mm Hg
1 atm

7. Learning Check A. What is 475 mmHg expressed in atm? 1) 475 atm
3) x 105 atm
B. The pressure in a tire is 2.00 atm. What is this
pressure in mmHg?
1) mmHg
2) mmHg
3) mmHg

8. Solution
A. What is 475 mmHg expressed in atm? 2) atm 475 mmHg x 1 atm = atm 760 mmHg B. The pressure in a tire is 2.00 atm. What is this pressure in mmHg? 2) 1520 mmHg 2.00 atm x 760 mmHg = 1520 mmHg 1 atm

9. Atmospheric Pressure Atmospheric pressure
is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth.
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10. 10 miles
0.2 atm
4 miles
0.5 atm
Sea level
1 atm

11. Altitude and Atmospheric Pressure
is about 1 atmosphere at sea level.
depends on the altitude and the weather.
is lower at higher altitudes, where the density of air is less.
is higher on a rainy day than on a sunny day.
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12. Barometer
A barometer
measures the pressure exerted by the gases in the atmosphere.
indicates atmospheric pressure as the height in mm of the mercury column.
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13. Learning Check
A. The downward pressure of the Hg in a barometer is _____ than (as) the pressure of the atmosphere.
1) greater 2) less 3) the same
B. A water barometer is 13.6 times taller than a Hg barometer (DHg = 13.6 g/mL) because
1) H2O is less dense than mercury.
2) H2O is heavier than mercury.
3) air is more dense than H2O.

14. Solution
A.The downward pressure of the Hg in a barometer is 3) the same (as) the pressure of the atmosphere. B. A water barometer is 13.6 times taller than a Hg barometer (DHg = 13.6 g/mL) because 1) H2O is less dense than mercury.

15. Temperature Conversion Equations
2 equations to use:
K = oC + 273
oC = K – 273

16. Practice Problem #1
240oC = ____K

17. Practice Problem #1
240oC = ____K
K = oC + 273
K =
K = 513

18. Practice Problem #2
350 K = ____ oC

19. Practice Problem #2 350 K = ____ oC oC = K – 273 oC = 350 – 273

20. Practice Problem #3
510 K = ____ oC

21. Practice Problem #3 510 K = ____ oC oC = K – 273 oC = 510 – 273

22. Practice Problem #4
20 oC = ____K

23. Practice Problem #4
20 oC = ____K
K = oC + 273
K =
K = 293