© 2013 Pearson Education, Inc. Chapter 7, Section 2 General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 7.2 Gas Pressure Chapter 7 Gases © 2013 Pearson Education, Inc. Lectures

© 2013 Pearson Education, Inc. Chapter 7, Section 2 Gas pressure  is the force acting on a specific area.  has units of atm, mmHg, torr, lb/in. 2, and kilopascals(kPa). 1 atm = 760 mmHg (exact) 1 atm = 760 torr (exact) 1 atm = 14.7 lb/in. 2 1 atm = kPa Gas Pressure 2

© 2013 Pearson Education, Inc. Chapter 7, Section 2 1. What is 475 mmHg expressed in atmospheres (atm)? A.475 atm B atm C.3.61 x 10 5 atm 2. The pressure in a tire is 2.00 atm. What is this pressure in mmHg? A mmHg B mmHg C mmHg Learning Check 3

© 2013 Pearson Education, Inc. Chapter 7, Section 2 1. What is 475 mmHg expressed in atmospheres (atm)? B atm 2. The pressure of a tire is measured as 2.00 atm. What is this pressure in mmHg? B.1520 mmHg Solution 4

© 2013 Pearson Education, Inc. Chapter 7, Section 2 Atmospheric pressure is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth. 5 Atmospheric Pressure

© 2013 Pearson Education, Inc. Chapter 7, Section 2 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. 6

© 2013 Pearson Education, Inc. Chapter 7, Section 2 Altitude and Atmospheric Pressure 7

© 2013 Pearson Education, Inc. Chapter 7, Section 2 Barometer A barometer measures the pressure exerted by the gases in the atmosphere by the height of mercury in the column (mmHg). A barometer: The pressure exerted by the gases in the atmosphere is equal to the downward pressure of a mercury column in a closed glass tube. 8

© 2013 Pearson Education, Inc. Chapter 7, Section 2 1.The downward pressure of the Hg in a barometer is _______ the pressure of the atmosphere. A. greater than B. less than C. the same as 2. A water barometer is 13.6 times taller than a mercury barometer (D Hg = 13.6 g/mL) because A. H 2 O is less dense. B. H 2 O is heavier. C. air is more dense than H 2 O. Learning Check 9

© 2013 Pearson Education, Inc. Chapter 7, Section 2 1. The downward pressure of the Hg in a barometer is the same as the pressure of the atmosphere. Answer: C 2. A water barometer is 13.6 times taller than a mercury barometer (D Hg = 13.6 g/mL) because H 2 O is less dense. Answer: A Solution 10