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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

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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?

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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

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

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

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Section 13.1 Describing the Properties of Gases A. Pressure 1 standard atmosphere = atm = mm Hg = 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?

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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

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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

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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

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

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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.

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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)

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

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

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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

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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)

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

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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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