4 Behavior of Gases

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Name Class DateSECTION 4Behavior of Gases continuedWhat Are the Gas Laws?Gases behave differently than solids or liquids do. Forexample, the volume of a gas can change due to pressure,but the volume of a solid or liquid generally cannot. Thegas laws describe how variables such as pressure, volume,and temperature affect the behavior of gases. Thegas laws will help you understand and predict the behaviorof gases in specific situations.READING CHECK2. Identify Boyle’s lawdescribes the relationshipbetween which two variables?PRESSURE AND VOLUMEA diver is swimming at a depth of 10 m below sealevel. An air bubble escapes from her mouthpiece. Asthe bubble rises to the surface, it gets bigger. When thebubble reaches the water’s surface, its volume is doubleits original size.This example shows the relationship between the volumeand pressure of a gas, also known as Boyle’s law.Boyle’s law is true for almost any gas, if temperatureand amount of gas are constant, or unchanged.Boyle’s LawFor a certain amount of gas at a constant temperature, thevolume of a gas decreases as the gas’s pressure increases.Likewise, the volume of a gas increases as the gas’s pressuredecreases.In mathematical terms:Boyle’s Law(initial pressure)(initial volume) = (final pressure)(final volume)P 1V 1= P 2V 2The figure below illustrates Boyle’s law. Both pistonscontain the same amount of gas at the same temperature.3. Identify What happens tovolume as pressuredecreases?If you lift the piston, pressuredecreases. The gas particlesspread farther apart, and thevolume increases.If you push the piston, pressureincreases. The gas particles arepushed closer together, and thevolume decreases.Copyright © by Holt, Rinehart and Winston. All rights reserved.Interactive Reader 62 States of Matter
Name Class DateSECTION 4Behavior of Gases continuedAPPLYING BOYLE’S LAWYou can use Boyle’s law to predict changes in the pressureor volume of a gas. Remember that Boyle’s law istrue only when the temperature and amount of gas do notchange.A balloon has a volume of 7.5 L at 100.0 kPa. As theballoon rises in the atmosphere, the gas inside expandsto a volume of 11 L. Assume the balloon is at a constanttemperature and the amount of gas does not change.What is the pressure when the volume is 11 L?READING CHECK4. Identify Under whatconditions does Boyle’s lawapply?The ballon on the left has a volume of 7.5 L and a pressure of 100 kPa. As the balloonrises, it becomes larger. The balloon’s new volume is 11 L. The temperatureand number of molecules inside the balloon stay the same.Step 1: List the given and unknownvalues.Step 2: Write the equation andrearrange to solve for the unknown.Given:V 1= 7.5 LP 1= 100.0 kPaV 2= 11 LP 1V 1= P 2V 2P 2= _P V 1 1V 2Step 3: Insert the known values and (100.0 kPa)(7.5 L)solve for the unknown value. P 2= __11 LP 2= 68 kPaUnknown:P 2MathSkills5. Calculate A 300 mLsample of hydrogen gas isat a pressure of 0.500 kPa.If the pressure increases to0.750 kPa, what will be thefinal volume of the sample?Assume that temperaturestays constant.PRESSURE AND TEMPERATURERecall that temperature is a measure of the averagekinetic energy of particles. As the particles of a substancemove faster, the substance’s temperature increases. Theparticles bump into each other and the sides of the containermore often, which increases pressure. Thus, astemperature increases, pressure increases. This is knownas Gay-Lussac’s law.Copyright © by Holt, Rinehart and Winston. All rights reserved.Interactive Reader 63 States of Matter
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4 Behavior of Gases

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