GASES Chapter 14

THREE STATES OF MATTER Solid Liquid Gas

General Properties of Gases Low densityLow density Expand infinitelyExpand infinitely Fill containers uniformly and completelyFill containers uniformly and completely Flow (molecules glide past each other)Flow (molecules glide past each other) Very compressibleVery compressible

How can the Kinetic Molecular Theory be used to explain the relationship that exists between the pressure and volume of a gas as described by Boyle's Law?

Boyle’s Law Relationship between pressure and volume.Relationship between pressure and volume. (temperature does not change)(temperature does not change) Pressure and Volume have an inverse relationshipPressure and Volume have an inverse relationship (As P↓ V↑)(As P↓ V↑) Why???Why??? Robert Boyle ( ). Son of Earl of Cork, Ireland.

Let’s Review: What causes gas pressure? –Collisions of gas particles against the container wall –The more collisions, the greater the pressure

What happens to the number of collisions if the volume of a container is decreased with no change in the number of gas particles? –Collisions will increase, therefore pressure will also increase

What happens to the number of collisions if the volume of a container is increased with no change in the number of gas particles? –Number of collisions will decrease (particles have further to travel to reach the walls of the container), therefore pressure will also decrease

Boyle’s Law Formula P 1 V 1 = P 2 V 2

Inverse Relationship

How Does It Work? Start conditionsEnd conditions P 1 = 5 atmP 2 = 10 atm V 1 = 10 mlV 2 = ? Plan: P 1 V 1 = P 2 V 2 Work the Plan: (5 atm)(10 ml) = (10 atm) X (5 atm) (10 ml) = X 10 atm 5 ml = X Same units

Practice P1 = 760 mm HgP2 = 600 mm Hg V1 = 15 mlV2 = ? Plan: P 1 V 1 = P 2 V 2 Work the Plan (760 mm Hg)(15 ml) = (600 mm Hg) X (760 mm Hg)(15 ml) = X 600 mm Hg 19 ml = X

Think About the Lab… What was happening as you used the syringe? –Removing air (gas particles) from the bell jar –Decreased pressure inside the bell jar Why did the balloon and marshmallow increase in volume? –Reduced pressure in the chamber allowed the volume of the trapped gases in the objects to expand (less force pushing against their “container” walls)

Why were there no visible changes in the cotton ball and the penny? –No trapped gases Why did the balloon return to its original volume while the marshmallow appeared to shrink? –Marshmallows are more porous, so some of the gases escaped with the syringe. The balloons ended with the same number of gas particles that they started with.

Why didn’t anything float when the pressure was decreased? 1.Gravity remained constant 2.The objects were all more dense than the air to begin with. After removing air particles from the chamber, the air density increased further, making the objects “heavier” in comparison.

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