Presentation on theme: "Compressibility Gases are easily compressed because of the space between the particles in a gas. The distance between particles in a gas is much greater."— Presentation transcript:




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1 Compressibility Gases are easily compressed because of the space between the particles in a gas. The distance between particles in a gas is much greater than the distance between particles in a liquid or solid. Under pressure, the particles in a gas are forced closer together.

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2 Factors Affecting Gas Pressure The amount of gas, volume, and temperature are factors that affect gas pressure.

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3 Factors Affecting Gas Pressure Four variables are generally used to describe a gas. The variables and their common units are pressure (P) in kilopascals volume (V) in liters temperature (T) in kelvins the number of moles (n).

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4 Factors Affecting Gas Pressure Amount of Gas You can use kinetic theory to predict and explain how gases will respond to a change of conditions. If you inflate an air raft, for example, the pressure inside the raft will increase.

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5 Factors Affecting Gas Pressure If the gas pressure increases until it exceeds the strength of an enclosed, rigid container, the container will burst.

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6 Factors Affecting Gas Pressure Volume You can raise the pressure exerted by a contained gas by reducing its volume. The more a gas is compressed, the greater is the pressure that the gas exerts inside the container.

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7 Factors Affecting Gas Pressure When the volume of the container is halved, the pressure the gas exerts is doubled.

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8 Factors Affecting Gas Pressure Temperature An increase in the temperature of an enclosed gas causes an increase in its pressure. As a gas is heated, the average kinetic energy of the particles in the gas increases. Faster-moving particles strike the walls of their container with more energy.

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9 Factors Affecting Gas Pressure When the Kelvin temperature of the enclosed gas doubles, the pressure of the enclosed gas doubles.

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10 Boyle’s Law: Pressure and Volume Boyle’s law states that for a given mass of gas at constant temperature, the volume of the gas varies inversely with pressure.

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11 Boyle’s Law: Pressure and Volume

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12 Charles’s Law: Temperature and Volume Charles’s law states that the volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant.

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13 Gay-Lussac’s Law: Pressure and Temperature Gay-Lussac’s law states that the pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant.

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14 The Combined Gas Law The combined gas law describes the relationship among the pressure, temperature, and volume of an enclosed gas.

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15 The Combined Gas Law The combined gas law allows you to do calculations for situations in which only the amount of gas is constant.

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16 Ideal Gas Law The gas law that includes all four variables—P, V, T, and n—is called the ideal gas law. The ideal gas constant (R) has the value 8.31 (L·kPa)/(K·mol).

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17 14.5

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19 for Sample Problem 14.5 Problem Solving 14.24 Solve Problem 24 with the help of an interactive guided tutorial.

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20 Ideal Gases and Real Gases Under what conditions are real gases most likely to differ from ideal gases?

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21 Ideal Gases and Real Gases a.There are attractions between the particles in an ideal gas. Because of these attractions, a gas can condense,or even solidify, when it is compressed or cooled.

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22 Ideal Gases and Real Gases Real gases differ most from an ideal gas at low temperatures and high pressures.

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23 Ideal Gases and Real Gases

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24 Dalton’s Law Dalton’s law of partial pressures states that, at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases.

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25 Dalton’s Law The contribution each gas in a mixture makes to the total pressure is called the partial pressure exerted by that gas.

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26 Dalton’s Law a.Three gases are combined in container T.

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27 Graham’s Law a.Bromine vapor is moving upward through the air in a graduated cylinder.

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28 Graham’s Law a.After several hours, the bromine has moved almost to the top of the cylinder.

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29 Graham’s Law Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout.

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30 Graham’s Law a.During effusion, a gas escapes through a tiny hole in its container. Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.

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31 Graham’s Law Graham’s law of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases.

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32 Graham’s Law Comparing Effusion Rates a.A helium filled balloon will deflate sooner than an air-filled balloon.

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33 Graham’s Law a.Helium atoms are less massive than oxygen or nitrogen molecules. So the molecules in air move more slowly than helium atoms with the same kinetic energy.

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34 Graham’s Law a.Because the rate of effusion is related only to a particle’s speed, Graham’s law can be written as follows for two gases, A and B.

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35 Graham’s Law a.Helium effuses (and diffuses) nearly three times faster than nitrogen at the same temperature.

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