Properties of Gases Gas Pressure

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.

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

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 = 760 mm Hg (exact) 1 atm = 760 torr 1 atm = 101 325 Pa 1 atm = 101.325 kPa 1 kPa = 7.501 mm Hg

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

Here is how you convert units 2.5 atm = _______ mmHg 2.5 atm x 760 mm Hg = 1900 mm Hg 1 atm

Learning Check A. What is 475 mmHg expressed in atm? 1) 475 atm 3) 3.61 x 105 atm B. The pressure in a tire is 2.00 atm. What is this pressure in mmHg? 1) 2.00 mmHg 2) 1520 mmHg 3) 22 300 mmHg

Solution A. What is 475 mmHg expressed in atm? 2) 0.625 atm 475 mmHg x 1 atm = 0.625 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

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. Copyright © 2009 by Pearson Education, Inc.

10 miles 0.2 atm 4 miles 0.5 atm Sea level 1 atm

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. Copyright © 2009 by Pearson Education, Inc.

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. Copyright © 2009 by Pearson Education, Inc.

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.

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.

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

Practice Problem #1 240oC = ____K

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

Practice Problem #2 350 K = ____ oC

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

Practice Problem #3 510 K = ____ oC

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

Practice Problem #4 20 oC = ____K

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