# Section 13.1 Describing the Properties of Gases 1.To learn about atmospheric pressure and how barometers work 2.To learn the units of pressure 3.To understand.

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Section 13.1 Describing the Properties of Gases 1.To learn about atmospheric pressure and how barometers work 2.To learn the units of pressure 3.To understand how the pressure and volume of a gas are related 4.To do calculations involving Boyle’s Law 5.To learn about absolute zero 6.To understand how the volume and temperature of a gas are related 7.To do calculations involving Charles’s Law 8.To understand how the volume and number of moles of a gas are related 9.To do calculations involving Avogadro’s Law Objectives

Section 13.1 Describing the Properties of Gases Gases Exert Pressure: What is Pressure? Pressure is defined as the force exerted divided by the area it acts over Pressure = Force/Area Typical Units are lbs/in 2 or kg/m 2 If a woman changes her shoes from sneakers to high heels does she exert a different pressure on the floor? Where does the pressure that a gas exerts come from?

Section 13.1 Describing the Properties of Gases A. Pressure Barometer – device that measures atmospheric pressure –Invented by Evangelista Torricelli in 1643 Measuring Atmospheric Pressure

Section 13.1 Describing the Properties of Gases A. Pressure –Changing weather conditions Atmospheric Pressure

Section 13.1 Describing the Properties of Gases A. Pressure –Changing altitude Atmospheric Pressure Record Sky Dive

Section 13.1 Describing the Properties of Gases A. Pressure 1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr = 101,325 Pa (1Pa = 1 N/m 2 ) Units of Pressure The air pressure on Everest is 0.3 atm. What is that measured using the other units?

Section 13.1 Describing the Properties of Gases A. Pressure Measurement of Pressure A manometer measures the pressure of a gas in a container Gas pressure is the force exerted by the collisions of gas particles with a surface

Section 13.1 Describing the Properties of Gases Robert Boyle’s experiment Around 1660 Boyle studied the relationship between the pressure and volume of a gas B. Pressure and Volume: Boyle’s Law

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law Draw a graph of V vs. P and also V vs. 1/P

Section 13.1 Describing the Properties of Gases Graphing Boyle’s results B. Pressure and Volume: Boyle’s Law

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law This graph has the shape of half of a hyperbola with an equation PV = k or V = k/P Volume and pressure are inversely proportional. –If one increases the other decreases.

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law Another way of stating Boyle’s Law is P 1 V 1 = P 2 V 2 (constant temperature and amount of gas) (WOC P480 Q7-10)

Section 13.1 Describing the Properties of Gases What makes this balloon fly? Balloon Launch

Section 13.1 Describing the Properties of Gases Graphing data for several gases C. Volume and Temperature: Charles’s Law

Section 13.1 Describing the Properties of Gases It is easier to write an equation for the relationship if the lines intersect the origin of the graph. C. Volume and Temperature: Charles’s Law –Use absolute zero for the temperature

Section 13.1 Describing the Properties of Gases These graphs are lines with an equation V = bT (where T is in kelvins) C. Volume and Temperature: Charles’s Law Volume and temperature are directly proportional. –If one increases the other increases by the same proportion. Another way of stating Charles’s Law is V 1 = V 2 T 1 T 2 (constant pressure and amount of gas)

Section 13.1 Describing the Properties of Gases D. Volume and Moles: Avogadro’s Law

Section 13.1 Describing the Properties of Gases D. Volume and Moles: Avogadro’s Law Volume and moles are directly proportional. –If one increases the other increases –V = an –constant temperature and pressure Another way of stating Avogadro’s Law is V 1 = V 2 n 1 n 2 (constant temperature and pressure)

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