GASESGASESChapter 14Chapter 14

THREE STATES OF THREE STATES OF MATTERMATTER

THREE STATES OF THREE STATES OF MATTERMATTER

Solid Liquid Gas

General Properties of General Properties of GasesGases

• Low densityLow density• Expand infinitelyExpand infinitely• Fill containers Fill containers

uniformly and uniformly and completelycompletely

• Flow (molecules glide Flow (molecules glide past each other)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 LawBoyle’s Law• Relationship Relationship

between pressure between pressure and volume.and volume.

• (temperature does (temperature does not change)not change)

• Pressure and Pressure and Volume have an Volume have an inverseinverse relationship relationship

• ((As P↓ V↑)As P↓ V↑)• Why???Why???

Robert Boyle Robert Boyle (1627-1691). Son (1627-1691). Son of Earl of Cork, of Earl of Cork, Ireland.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

FormulaP1V1 = P2V2

Inverse Relationship

How Does It Work?Start conditions End conditions

P1 = 5 atm P2 = 10 atm

V1 = 10 ml V2 = ?

Plan: P1V1 = P2V2

Work the Plan: (5 atm)(10 ml) = (10 atm) X

(5 atm) (10 ml) = X

10 atm5 ml = X

Same units

Practice

• P1 = 760 mm Hg P2 = 600 mm Hg• V1 = 15 ml V2 = ?

Plan: P1V1 = P2V2

Work thePlan (760 mm Hg)(15 ml) = (600 mm Hg) X (760 mm Hg)(15 ml) = X

600 mm Hg19 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.

• All images in this slide show are part of public domain and can freely used.