CHAPTER 12 GASES AND KINETIC-MOLECULAR THEORY

[Pages:30]CHAPTER 12 GASES AND KINETIC-MOLECULAR

THEORY

1. Pressure 2. Boyle's Law: The V-P Relationship 3. Charles' Law: The V-T Relationship 4. Standard T&P 5. The Combined Gas Law Equation 6. Avogadro's Law and the Standard Molar Volume 7. Summary of Gas Laws: The Ideal Gas Equation 8. Dalton's Law of Partial Pressures 9. The Kinetic-Molecular Theory 10. Diffusion and Effusion of Gases 11. Real Gases: Deviations from Ideality

1

Pressure

{ Pressure is force per unit area.

z lb/in2

z N/m2

{ Gas pressure as most people think of it.

{ Atmospheric pressure is measured using a barometer.

{ Definitions of standard pressure

z 76 cm Hg

z 760 mm Hg

z 760 torr

z 1 atmosphere

z 101.3 kPa

Hg density = 13.6 g/mL

2

Boyle's Law: The Volume-Pressure Relationship

{ V 1/P or { V= k (1/P) or PV = k { P1V1 = k1 for one sample of a gas. { P2V2 = k2 for a second sample of a

gas. { k1 = k2 for the same sample of a gas

at the same T. { Thus we can write Boyle's Law

mathematically as P1V1 = P2V2

3

Boyle's Law: The Volume-Pressure Relationship

{ At 25oC a sample of He has a volume of 4.00 x 102 mL under a pressure of 7.60 x 102 torr. What volume would it occupy under a pressure of 2.00 atm at the same T?

P1 V1 = P2 V2

V2

=

P1 V1 P2

= (760 torr )(400 mL)

1520 torr

= 2.00 ?102 mL 4

Charles' Law: The Volume-Temperature Relationship; The Absolute Temperature Scale

35

30

25

20

Volume (L)

vs.

15

Temperature (K)

10

Gases liquefy

before reaching 0K

5

0 0 50 100 150 200 250 300 350 400

absolute zero = -273.15 0C

5

Charles' Law: The Volume-Temperature Relationship; The Absolute Temperature Scale

{ Charles's law states that the volume of a gas is directly proportional to the absolute temperature at constant pressure.

z Gas laws must use the Kelvin scale to be correct.

{ Relationship between Kelvin and centigrade.

K = oC + 273

6

Charles' Law: The Volume-Temperature Relationship; The Absolute Temperature Scale

{ Mathematical form of Charles' law.

V T or V = kT or V = k T

V1 = k and V2 = k however the k's are equalso

T1

T2

V1 = V2 in the most useful form T1 T2

7

Charles' Law: The Volume-Temperature Relationship; The Absolute Temperature Scale

{ A sample of hydrogen, H2, occupies 1.00 x 102 mL at 25.0oC and 1.00 atm. What volume would it occupy at 50.0oC under the same pressure?

T1 = 25 + 273 = 298

T2 = 50 + 273 = 323

V1 T1

=

V2 T2

V 2

=

V1T2 T1

1.00 ?102 mL ? 323 K

V2 =

298 K

= 108 mL

8

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