1 Chapter 6 The States of Matter 6.6 The Gas Laws

2 Definitions Gas Law – a mathematical relationship that describes the behavior of gases as they are mixed, subjected to pressure or temperature changes, or allowed to diffuse. Pressure – A force per unit area of surface on which the force acts. In measurements and calculations involving gases, it is often expressed in units related to measurements of atmospheric pressure. Standard Atmosphere – The pressure needed to support a 760 mm column of Hg in a barometer tube. Torr – The pressure needed to support a 1 mm column of Hg in a barometer tube. Absolute Zero – The temp at which all motion stops; a value of 0 on the Kelvin scale.

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

4 Gas pressure is described as a force acting on a specific area. Pressure (P) = Force Area Has units of atm, mm Hg, torr, lb/in. 2 and kilopascals(kPa). 1 atm = 760 mm Hg (exact) 1 atm = 760 torr 1 atm = 14.7 lb/in. 2 1 atm = kPa Gas Pressure

5 A. What is 475 mm Hg expressed in atm? 1) 475 atm 2) atm 3) 3.61 x 10 5 atm B. The pressure in a tire is 2.00 atm. What is this pressure in mm Hg? 1) 2.00 mm Hg 2) 1520 mm Hg 3) mm Hg Learning Check

6 Solution A. What is 475 mm Hg expressed in atm? 2) atm 475 mm Hg x 1 atm = atm 760 mm Hg B. The pressure of a tire is measured as 2.00 atm. What is this pressure in mm Hg? 2) 1520 mm Hg 2.00 atm x 760 mm Hg = 1520 mm Hg 1 atm

7 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.

8 Altitude and Atmospheric Pressure Atmospheric pressure is about 1 atmosphere at sea level. depends on the altitude and the weather. is lower at high altitudes where the density of air is less. is higher on a rainy day than on a sunny day.

9 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.

10 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 (D Hg = 13.6 g/mL) because 1) H 2 O is less dense than mercury. 2) H 2 O is heavier than mercury. 3) air is more dense than H 2 O. Learning Check

11 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 (D Hg = 13.6 g/mL) because 1) H 2 O is less dense than mercury. Solution