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Three States of Matter

Physical Properties of Gases (Page 161)

Because of the great distance between particles,

gas behavior is fundamentally different from the

other phases

Gases assume the volume and shape of their

container

Gases have lower densities and are more

compressible than solids and liquids

Gases will mix uniformly when placed in the same

container

The Gaseous Elements

(at room temperature)

Common Gaseous Compounds

NH3 ammonia

HCl hydrogen chloride

CO2 carbon dioxide

SO2 sulfur dioxide

Be sure you are familiar with all of the gaseous

substances listed in table 5.1 on page 161

Pressure

Gases exert pressure on objects in their

surroundings.

Pressure is caused by collisions between gas

particles and the objects with which they are in

contact.

Pressure is the force exerted on a unit of area.

Pressure Force

area

Atmospheric pressure is caused by the weight of

air in the earths atmosphere

Atmospheric pressure pushes equally in all

directions

It is measured with a barometer.

Making a Barometer

Pressure Force

area

First mercury barometer made by Evangilista

Torricelli in 1643

The weight of the column of mercury is equal to

the force exerted by the atmosphere

Normal atmospheric pressure

760 mm of Hg

Units for Normal Atmospheric Pressure

Patm Normal Atm Pressure 760 mm Hg.

Patm 760 torr.

1.00 mm Hg 1.00 torr.

Patm 1.00 atm 760 torr.

Patm 14.7 lbs/in2

SI Units for Normal Atmospheric Pressure

Pressure Force

area

1 pascal 1 newton of force

1 meter 2

Patm 101.3 kilopascals (kPa)

Patm 760 mm Hg 101.3 kPa

The Manometer

A manometer measures gas pressure as a difference

in Hg column heights.

Closed-end manometer difference in column

heights gives absolute pressure.

Open-end manometer difference in column heights

gives difference between gas sample and

atmospheric pressures

Open-end Manometer

Patm gt Pgas

Pgas h

Patm

Patm - h

Pgas

748 mm Hg - 78 mm Hg

Pgas

670 mm Hg

Pgas

Open-end Manometer

Pgas gt Patm

Patm h

Pgas

748 mm Hg 57 mm Hg

Pgas

805 mm Hg

Pgas

Closed-end Manometer

Pgas gt 0

h 0 torr

Pgas

85 mm Hg

Pgas

The Four Gas Parameters

- Four parameters are needed to define the

physical condition or state of any gas - Temperature (T)
- Pressure (P)
- Volume (V)
- Amount of gas (moles n)
- Equations relating these variables are known as

the gas laws.

The Gas Laws

Boyles Law (P-V Relationship)

Charles Law (T-V Relationship)

Avogadros Law (n-V Relationship)

Gay-Lussacs Law (P-T Relationship)

The two parameters not being studied are held

constant

Boyles Law

Temperature and amount remain constant

Boyles Law

P a 1/V

P K /V

PV K

Temperature and amount remain constant

P1V1 P2V2

BOYLES LAW (P-V RELATIONSHIP)

The volume of a fixed amount of gas maintained at

constant temperature is inversely proportional to

pressure.

(T and n constant)

Charless Law

V a T

V K T

V/T K

Pressure and amount remain constant

- Charless Law and Absolute Zero

K oC 273

oC K - 273

Absolute zero is the temperature at which there

is no energy.

-273.15oC

Gay-Lussacs Law

P a T

P K T

P/T K

Volume and amount remain constant

Avogadros Law

V a n

V K n

V/n K

Pressure and temperature remain constant

Ideal Gas Law

Boyles Law

Charless Law

Avagadros Law

Expressed Mathematically

Finding the Value of R

Standard temperature 273.15 K (0C) Standard

Pressure 1 atm

At STP 1 mole of any gas occupies 22.414 L

solving

gives

Some Values of the Gas Constant R

R 0.08206 Latm

mol K

R 62.36 Ltorr

mol K

R 8.31 LkPa

mol K

Single State Problem

A 12.25 L cylinder contains 75.5 g of neon at

24.5 oC. Determine the pressure in the cylinder.

What type of problem is this?

Only one set of conditions

A 12.25 L cylinder contains 75.5 g of neon at

24.5 oC. Determine the pressure in the cylinder.

P nRT V

PV nRT

(3.74 mol)(62.4Ltorr)(297.5K) (12.25 L)

molK

?

P V n R T

12.25 L

mol

5667.7 torr

75.5 g mol

3.74

20.18 g

5670 torr

62.4 Ltorr molK

How many atmospheres is this?

24.5 273 297.5 K

Double State Problem

A balloon contains helium gas with a volume of

2.60 L at 25 oC and 768 mmHg. If the balloon

ascends to an altitude where the helium pressure

is 590 mmHg and the temperature is 15 oC, what is

the volume of the balloon?

What type of problem is this?

There are 2 sets of conditions.

A balloon contains helium gas with a volume of

2.60 L at 25 oC and 768 mmHg. If the balloon

ascends to an altitude where the helium pressure

is 590 mm Hg and the temperature is 15 oC, what

is the volume of the balloon?

P1 V1 T1 n1

P2 V2 T2 n2

768 torr

590 torr

2.60 L

?

25 273 298 K

15 273 288 K

(768 torr)(2.60 L)(288 K) (590

torr)(298 K)

3.27 L

A 2.50 gram sample of a solid was vaporized in a

505 mL vessel. If the vapor pressure of the

solid was 755 mmHg at 155 oC, what is the

molecular weight of the solid?

molecular weight molar mass g/mol g ? mol

..so if we can find grams and moles and divide....

...we already have grams!! Were halfway there!

P V n R T

755 torr

n PV RT

0.505 L

755 torr 0.505 L molK___________

62.4 Ltorr

428 K

62.4 Ltorr molK

0.01428 mol

155 273 428 K

NOW 2.50 g g

0.01428 mol mol

175.1