I. Physical Properties

Ch. 11 - Gases

A. Kinetic Molecular TheoryParticles in an ideal gas…

• have no volume.• have elastic collisions. • are in constant, random, straight-

line motion.• don’t attract or repel each other.• have an avg. KE directly related

to Kelvin temperature.

B. Real GasesParticles in a REAL gas…

• have their own volume• attract each other

Gas behavior is most ideal…• at low pressures• at high temperatures• in nonpolar atoms/molecules

C. Characteristics of GasesGases expand to fill any container.

• random motion, no attractionGases are fluids (like liquids).

• no attractionGases have very low densities.

• no volume = lots of empty space

C. Characteristics of GasesGases can be compressed.

• no volume = lots of empty spaceGases undergo diffusion & effusion.

• random motion

D. Temperature

ºF

ºC

K

-459 32 212

-273 0 100

0 273 373

32FC 95 K = ºC + 273

Always use absolute temperature (Kelvin) when working with gases.

E. Pressure

areaforcepressure

Which shoes create the most pressure?

E. PressureBarometer

• measures atmospheric pressure

Mercury Barometer

Aneroid Barometer

E. PressureManometer

• measures contained gas pressure

U-tube Manometer Bourdon-tube gauge

E. Pressure

2mNkPa

KEY UNITS AT SEA LEVEL101.325 kPa (kilopascal)

1 atm

760 mm Hg

760 torr

14.7 psi

F. STP

Standard Temperature & Pressure

0°C 273 K

1 atm 101.325 kPa-OR-

STP

II. The Gas Laws

Ch. 11 - Gases

A. Boyle’s LawThe pressure and volume

of a gas are inversely related • at constant mass & temp

P

V

PV = k

A. Boyle’s Law

kTV

V

T

B. Charles’ LawThe volume and absolute

temperature (K) of a gas are directly related • at constant mass &

pressure

B. Charles’ Law

kTP

P

T

C. Gay-Lussac’s LawThe pressure and absolute

temperature (K) of a gas are directly related • at constant mass &

volume

= kPVPTVT

PVT

D. Combined Gas Law

P1V1

T1=

P2V2

T2

P1V1T2 = P2V2T1

GIVEN:V1 = 473 cm3

T1 = 36°C = 309KV2 = ?T2 = 94°C = 367K

WORK:P1V1T2 = P2V2T1

E. Gas Law ProblemsA gas occupies 473 cm3 at 36°C.

Find its volume at 94°C.

CHARLES’ LAWT V

(473 cm3)(367 K)=V2(309 K)

V2 = 562 cm3

GIVEN:V1 = 100. mLP1 = 150. kPaV2 = ?P2 = 200. kPa

WORK:P1V1T2 = P2V2T1

E. Gas Law ProblemsA gas occupies 100. mL at 150.

kPa. Find its volume at 200. kPa.

BOYLE’S LAWP V

(150.kPa)(100.mL)=(200.kPa)V2

V2 = 75.0 mL

GIVEN:V1 = 7.84 cm3

P1 = 71.8 kPaT1 = 25°C = 298 KV2 = ?P2 = 101.325 kPaT2 = 273 K

WORK:P1V1T2 = P2V2T1

(71.8 kPa)(7.84 cm3)(273 K)=(101.325 kPa) V2 (298 K)

V2 = 5.09 cm3

E. Gas Law Problems A gas occupies 7.84 cm3 at 71.8 kPa &

25°C. Find its volume at STP.

P T VCOMBINED GAS LAW

GIVEN:P1 = 765 torrT1 = 23°C = 296KP2 = 560. torrT2 = ?

WORK:P1V1T2 = P2V2T1

E. Gas Law ProblemsA gas’ pressure is 765 torr at 23°C.

At what temperature will the pressure be 560. torr?

GAY-LUSSAC’S LAWP T

(765 torr)T2 = (560. torr)(296K)

T2 = 217 K

END OF QUIZ I MATERIAL

III. Ideal Gas Law

Ch. 11 - Gases

knV

V

n

A. Avogadro’s Principle Equal volumes of gases contain

equal numbers of moles• at constant temp & pressure• true for any gas

PVTVn

PVnT

A. Ideal Gas Law p. 384

= kUNIVERSALAS CONSTANT

R=0.0821 Latm/molKR = 62.4 Lmm Hg/molK (torr)

R=8.315 dm3kPa/molK

= R

You don’t need to memorize these values!

Merge the Combined Gas Law with Avogadro’s Principle:

A. Ideal Gas Law

UNIVERSAL GAS CONSTANT

R=0.0821 Latm/molKR = 62.4 Lmm Hg/molK (torr)

R=8.315 dm3kPa/molK

PV=nRT

You don’t need to memorize these values!

GIVEN:P = ? atmn = 0.412 molT = 16°C = 289 KV = 3.25 LR = 0.0821Latm/molK

WORK:PV = nRT

P(3.25)=(0.412)(0.0821)(289) L mol Latm/molK K

P = 3.01 atm

C. Ideal Gas Law Problems Calculate the pressure in atmospheres

of 0.412 mol of He at 16°C & occupying 3.25 L.

GIVEN:V = ?m = 85 gT = 25°C = 298 KP = 104.5 kPaR = 8.315 dm3kPa/molK

C. Ideal Gas Law Problems Find the volume of 85 g of O2 at 25°C

and 104.5 kPa.

n= 2.7 mol

WORK:85 g 1 mol = 2.7 mol 32.00 g

PV = nRT(104.5)V=(2.7) (8.315) (298) kPa mol dm3kPa/molK K

V = 64 dm3

Let’s Practice!! Handout p.24Things to remember:OMIT 5 & 6Convert temperatures to Kelvin

(add 273)Convert all volumes to Liters (mL to

L divide by 1000)Use R value that matches pressure

unit