Chapter05_LEC - Chapter 5 Gases Roy Kennedy Massachusetts...

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Unformatted text preview: Chapter 5 Gases Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA 2008, Prentice Hall Chemistry: A Molecular Approach , 1 st Ed. Nivaldo Tro Tro, Chemistry: A Molecular Approach 2 Atmospheric Pressure pressure is the force exerted over an area Area Force Pressure = Tro, Chemistry: A Molecular Approach 3 Gases Pushing Tend to form homo mixtures Low densities D/n have a fixed shape or volume gas molecules are constantly in motion as they move and strike a surface, they push on that surface push = force if we could measure the total amount of force exerted by gas molecules hitting the entire surface at any one instant, we would know the pressure the gas is exerting pressure = force per unit area Tro, Chemistry: A Molecular Approach 4 The Effect of Gas Pressure whenever there is a pressure difference, a gas will flow from area of high pressure to low pressure the bigger the difference in pressure, the stronger the flow of the gas if there is something in the gass path, the gas will try to push it along as the gas flows Tro, Chemistry: A Molecular Approach 5 Atmospheric Pressure Effects the higher up in the atmosphere, the lower the atmospheric pressure Tro, Chemistry: A Molecular Approach 6 The Pressure of a Gas result of the constant movement of the gas molecules and their collisions with the surfaces around them the pressure of a gas depends on several factors number of gas particles in a given volume volume of the container average speed of the gas particles Tro, Chemistry: A Molecular Approach 7 Measuring Air Pressure use a barometer Measure relative pressure in 1 atm Adjusts for the difference in altitude column of mercury supported by air pressure Monometers are also used gravity Tro, Chemistry: A Molecular Approach 8 Common Units of Pressure Unit Average Air Pressure at Sea Level pascal (Pa), 101,325 kilopascal (kPa) 101.325 atmosphere (atm)/bar 1 (exactly) millimeters of mercury (mmHg) 760 (exactly) inches of mercury (inHg) 29.92 torr (torr) 760 (exactly) pounds per square inch (psi, lbs./in 2 ) 14.7 2 m N 1 Pa 1 = Example 5.1 A high-performance bicycle tire has a pressure of 132 psi. What is the pressure in mmHg? since mmHg are smaller than psi, the answer makes sense 1 atm = 14.7 psi, 1 atm = 760 mmHg 132 psi mmHg Check: Solution: Concept Plan: Relationships: Given: Find: psi 14.7 atm 1 mmHg 10 .82 6 atm 1 mmHg 760 psi 14.7 atm 1 psi 132 3 = atm 1 mmHg 760 psi atm mmHg Tro, Chemistry: A Molecular Approach 10 Manometers the pressure of a gas trapped in a container can be measured with an instrument called a manometer manometers are U-shaped tubes, partially filled with a liquid, connected to the gas sample on one side and open to the air on the other a competition is established between the pressure of the atmosphere and the gas the difference in the liquid levels is a measure of the difference in pressure between the gas and the atmosphere Tro, Chemistry: A Molecular Approach...
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Chapter05_LEC - Chapter 5 Gases Roy Kennedy Massachusetts...

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