Unit 2 - Chapter 5 - Zumbahl Chemistry 6th Edition Chapter...

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Zumbahl: Chemistry 6 th Edition Chapter 5: Gases 5.1 Pressure ∙One of the most obvious properties of a gas it that it exerts pressure on its surroundings. ∙As a gas, water occupies 1200x as much space as it does as a liquid at 25°C and atmospheric pressure. Barometer – a device for measuring atmospheric pressure. ∙Invented by Evangelista Torricelli – student of Galileo. ∙Atmospheric pressure results from the mass of air being pulled toward the center of earth by gravity. ∙In other words, atmospheric pressure results from the weight of the air. ∙Atmospheric pressure varies when: ∙Weather conditions changes. ∙Variation in altitude or height. ∙Because instruments used for measuring pressure often contain mercury, the most commonly used units for pressure are based on the height of the mercury column (in millimeters) that the gas pressure can support. ∙Example of an instrument: Manometer – a device for measuring the pressure of a gas in a container. mm Hg (millimeter of mercury) – unit of pressure. ∙1 mm Hg = 1 torr. torr – another name for mm Hg. ∙760 mm Hg = 760 torr. Standard atmosphere (atm) – a unit of pressure equal to 760 mm Hg. ∙1 standard atmosphere = 1 atm = 760 mm Hg = 760 torr. ∙Pressure is defined as force per unit area. ∙Pressure = force area Pascal – the SI unit of pressure equal to newtons per meter squared. ∙1 standard atmosphere = 101,325 Pa or 10 5 Pa. ∙1 atm = 760 mm Hg = 760 torr = 101,325 Pa = 29.92 in Hg = 14.7 lb/in 2 5.2 Gas Laws of Boyle, Charles, and Avogadro Boyle’s law – the volume of a given sample of gas at constant temperature varies inversely with the pressure. ∙PV = k k is a constant for a given sample of air at a specific temperature. ∙Therefore, V ∞ 1/P at constant temperature. ∙Can also be written as: ∙P 1 V 1 = P 2 V 2 ∙One common use of Boyle’s law is to predict the new volume of gas when pressure is changed at constant temperature, or vice versa. ∙For calculations, assume that gases obey Boyle’s law (unless stated otherwise). ∙The gases that strictly obey Boyle’s law are ideal gases or perfect gases. ∙The conditions of ideal gas or perfect gas: 1. Has zero volume
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Zumbahl: Chemistry 6 th Edition 2. Consider all gas molecules to be the same. 3. Little attraction or repulsion between gas molecules. 4. “Perfect elastic collusion” – no loss in energy. ∙To help eliminate errors, make it habit to check whether an answer to a problem makes physical sense. Charles’s law – the volume of a given sample of gas at constant pressure is directly proportional to the temperature in kelvins.
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