1

Kinetic Theory of Gases

consists of small particles thatmove rapidly in straight lines.

essentially no attractive (or repulsive) forces.

are very far apart.very small volumes compared

volume of container occupied kinetic energies

increase with increased temperature.

2

Properties that describe a gas

four properties: pressure (P), volume(V), temperature(T), and amount(n).

3

What is gas pressure?

force acting on a specific area. Pressure (P) = Force

Areaunits of atm, mm Hg, torr

1 atm = 760 mm Hg1 atm = 760 torr

4

What is atmospheric pressure?

pressure exerted by a column of airfrom top of atmosphere

to surface of earth1 atmosphere at sea leveldepends on altitude and weatherlower at high altitudes

density of air less. higher on a rainy day

than sunny day

5

What is a barometer?

measures pressure exerted by gases in atmosphere.

indicates byheight in mm of mercury column.

6

Boyle’s Law (pressure-volume) law

pressure of a gas inversely related to its volumewhen T and n are constant

volume decreasespressure increases

product P x V constant as long as T and n unchanged

P1V1 = P2V2 (T, n constant)can be solved for any factor

7

Breathing, an example

During inhalation lungs expandpressure in lungs decreasesair flows towards lower pressure in

lungsDuring exhalation

lung volume decreasespressure within lungs increasesair flows from higher pressure in

lungs to outside

8

Calculation with Boyle’s Law

Freon-12, CCl2F2, is used in refrigeration

systems. What is the new volume (L) of a 8.0

L sample of Freon gas initially at 550 mm Hg

after its pressure is changed to 2200 mm Hg at

constant T?1. Set up a data table:

Conditions 1 Conditions 2

P1 = 550 mm Hg P2 = 2200 mm HgV1 = 8.0 L V2 =

?

9

Calculation with Boyle’s law (continued)

2. When pressure increases, volume decreases.Solve Boyle’s Law for V2: P1V1 = P2V2

V2 = V1 x P1

P2 V2 = 8.0 L x 550 mm Hg = 2.0 L

2200 mm Hg

10

Learning Check

For a cylinder containing helium gas

indicate if cylinder A or cylinder Brepresents the new volume for thefollowing changes (n and T areconstant).

1) pressure decreases2) pressure increases

11

Learning Check

A sample of oxygen gas has a volume of

12.0 L at 600. mm Hg. What is the new

pressure when the volume changes to

36.0 L? (T and n constant).

A) 200. mm Hg B) 400. mm Hg C) 1200 mm Hg

12

Solution A) 200. mm Hg

Data table Conditions 1 Conditions 2P1 = 600. mm Hg P2 = ???V1 = 12.0 L V2 = 36.0 L

P2 = P1 x V1 V2

= 600. mm Hg x 12.0 L 36.0 L = 200. mm Hg

13

Charles’ law temperature -volume

Charles’ Law,Kelvin temperature of a gas

directly related to volume P and n are constanttemperature of a gas increases

volume increasesV1 T1= V2 T2

(P and n constant)rearranging Charles’ Law

Calculations using charles’ law

A balloon has a volume of 785 mL at21°C. If the temperature drops to

0°C, what is the new volume of the balloon(P constant)? 1. Set up data table:Conditions 1 Conditions 2V1 = 785 mL V2 = ?T1 = 21°C = 294 K T2 = 0°C =

273 KKelvin (K) temperature in gas

calculations.

15

Calculations Using Charles’ Law (continued)

2. Solve Charles’ law for V2:

V1 = V2

T1 T2

V2 = V1 x T2

T1

V2 = 785 mL x 273 K = 729 mL 294 K

16

Learning Check

A sample of oxygen gas has a volume of

420 mL at a temperature of 18°C. At

what temperature (in °C) will thevolume of the oxygen be 640 mL

(P andn constant)?

1) 443°C2) 170°C 3) - 82°C

17

What is STP?

volumes of gases can be compared at STP, Standard Temperature andPressure,

the same temperature.Standard temperature (T) 0°C or 273 K

the same pressure. Standard pressure (P) 1 atm (760 mm Hg)

18

What is Molar volume?

standard temperature and pressure (STP), 1 mole of a gas occupies a volume of 22.4 L, its molar volume

used to form conversion factors22.4 L and 1 mole 1 mole 22.4 L

19

Partial Pressure (Dalton’s Law) pressure of each gas in mixture. pressure gas would exert if

itself in container pressure depends on total number of gas

particles not on types of particles

total pressure exerted by gases mixture sum of partial pressures of gases

Calculate the sum of the partial pressures.Ptotal = PO2 + PHe

Ptotal = 342 mm Hg + 855 mm Hg

= 1197 mm Hg

20

Scuba Diving-!When a scuba diver dives,

increased pressure causes N2(g) to dissolve in blood.

If diver rises too fast, dissolved N2 will form bubbles in

blood"the bends"

Helium, does not dissolve in blood, mixed with O2 to prepare breathing

mixtures for deep descents.

21

Gases We Breathecontains N2 and O2 & smallamounts of other gasesO2 enters blood, while CO2 from

blood releasedtissues, O2 enters cells,

release CO2 into blood. O2 flows into tissues

partial pressure of O2 higher in blood, lower in tissues

CO2 flows out of the tissues partial pressure of CO2 is higher in tissues, lower in the blood