Chem 122 midterm 1

Chem 122 midterm 1 - Chemistry 122 Midterm 1 Study Guide.1...

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Chemistry 122 Midterm 1 Study Guide
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Chapter 10 10.1- Characteristics of Gases Gases behave quite similarly as far as their physical properties are concerned (although chemical properties differ). Only few elements exist as a gas under ordinary conditions of temperature and pressure: The noble gases (He, Ne, Ar, Kr, and Xe) & H 2 , N 2 , O 2 , F 2 , and Cl 2 . A gas fills spontaneously to fill the volume of its container, gases are highly compressible- when pressure is applied the volume readily decreases. Gases form homogenous mixtures with each other regardless of the identities or relative proportions of the component gases. Each molecule behaves as though the other is not present. In contrast to gases, liquids are held relatively close together and the attractive forces among the molecules keep the liquid together. 10.2 – Pressure Readily measured properties of a gas are temperature, volume, and pressure. Pressure conveys the idea of a force, a push that tends to move something in a given direction. Pressure, P, is, in fact, the force, F, that acts on a given area, A. o P=F/A Gases exert a pressure on any surface which they are in contact. Gravity causes the atmosphere as a whole to press down on the Earth’s surface, creating an atmospheric pressure. We can calculate the magnitude of the atmospheric pressure as follows: The force, F, exerted by an object is the product of its mass, m, times its acceleration, a; that is F = ma. o The acceleration given by Earth’s gravity to any object located near Earth’s surface is 9.8 m/s 2 . o The SI unit for force is kg-m/s 2 Which is 1N (1 Newton) The SI unit of pressure is N/m 2 o This was given the name Pascal (Pa) o 1 bar = 10 5 Pa The actual atmospheric pressure at any one given time depends on the altitude and weather conditions Atmospheric pressure is measured by a barometer (created by Evangelista Torricelli), which is a device that uses mercury levels to determine pressure. Pressure decreases as altitude increases o Was proven that the atmosphere has weight Standard atmospheric pressure, which corresponds to the typical pressure at sea level, is the pressure sufficient to support a column of mercury 760 mm high. o 1 atm = 760 mmHg = 760 torr = 1.01325 x 10 5 Pa = 101.325 kPa
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10.3 – The Gas Laws Four variables are needed to define the physical condition, or state, of a gas: Temperature (T), pressure (P), volume (V), and the amount of gas, which is usually expressed as the number of moles (n). The equations that express the relationships among T, P, V, and n are known as the gas laws. When volume is decreased, pressure of a gas increases Boyle’s Law- the volume of a fixed quantity of gas at constant temperature is is inversely proportional to the pressure.
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