Figure 4.12

A summary of terminology for oxidation-

reduction (redox) reactions

X Y

e-

transfer

or shift of

electrons

X Loses Electron(s) Y Gains Electron(s)

X is Oxidized Y is Reduced

X is the reducing agent Y is the oxidizing agent

X increases its

oxidation number

Y decreases its

oxidation number

Table 4.3 Rules for Assigning an Oxidation Number (O.N.)

1. For an atom in its elemental form (Na, O2, Cl2, etc.): O.N. = 0

2. For a monoatomic ion: O.N. = ion charge

3. The sum of O.N. values for the atoms in a compound equals zero. The

sum of O.N. values for the atoms in a polyatomic ion equals the ion’s charge.

General rules

Rules for specific atoms or periodic table groups

1. For Group 1A(1): O.N. = +1 in all compounds

2. For Group 2A(2): O.N. = +2 in all compounds

3. For hydrogen: O.N. = +1 in combination with nonmetals

4. For fluorine: O.N. = -1 in combination with metals and boron

6. For Group 7A(17): O.N. = -1 in combination with metals, nonmetals

(except O), and other halogens lower in the group

5. For oxygen: O.N. = -1 in peroxides

O.N. = -2 in all other compounds(except with F)

Figure 4.14 Combining elements to form an ionic compound

Figure 4.15 Decomposing a compound to its elements

Figure 4.18 Displacing one metal with another

An alternate definition of redox • Oxidation is gain of oxygen or loss of hydrogen

• Reduction is loss of oxygen or gain of hydrogen.

• Ex.

CH

O

H

O O CH O H

O

Carbon gains bonds to oxygen

and loses bonds to hydrogen.

The carbon is oxidized.

Oxygen gains bonds to hydrogen. It is reduced.

CH2O + O2 CH2O2

0 +1 0 +2 +1 -2 -2

Determining number of electrons transferred

• In a redox reaction, electrons gained = electrons lost.

How many electrons are gained/lost in the following

reactions?

2MnO4- (aq) + 5C2O4

2- (aq) + 16H+ (aq)

2 Mn2+ (aq) + 10CO2 (g) + 8H2O (l)

+7

+2

+3

+4

3Ca + N2 Ca3N2

1 e- per C x 10 C = 10 e-

5 e- per Mn x 2 Mn = 10 e-

0 0 +2 -3

2 e- per Ca x 3 Ca = 6 e-

3 e- per N x 2 N = 6 e-

Gases

You have them

Figure 5.1 The three states of matter.

Figure 5.2: A

mercury

barometer

Kelter, Mosher and Scott, Chemistry: The Practical Science, 1/e. Copyright © 2008 by Houghton Mifflin Company. Reprinted with permission.

Pressure due to fluid column

column of Area

column ofmass CombinedP

5 | 13

• Pressure, P

• The force exerted per unit area

• It can be given by two equations:

• The SI unit for pressure is the pascal, Pa.

(pascal)Pa

sm

kgm

s

m

m

kg223

dgh P A

FP

(pascal)Pa

sm

kg

m

s

mkg

22

2

Assume constant dens., gravity

0

100

200

300

400

500

600

700

800

0 10000 20000 30000 40000 50000 60000 70000 80000

Baro

metr

ic P

ressu

re (

To

rr)

Altitude ( ft)

Barometric Pressure vs Altitude

Table 5.2 Common Units of Pressure

Atmospheric Pressure Unit Scientific Field

chemistry atmosphere(atm) 1 atm

pascal(Pa);

kilopascal(kPa)

1.01325x105Pa;

101.325 kPa

SI unit; physics, chemistry

millimeters of

mercury(Hg)

760 mmHg chemistry, medicine, biology

torr 760 torr chemistry

pounds per square

inch (psi or lb/in2)

14.7lb/in2 engineering

bar 1.01325 bar

1 bar = 100,000 Pa

meteorology, chemistry,

physics

Figure 5.5 The relationship between volume and

the pressure of a gas.

Figure 5.6

The relationship between volume

and the temperature of a gas.

Standard Molar Volume

Figure 5.17: Finding the

vapor density of a

substance

Three flasks are filled with He, Ne, and Ar

respectively. Initially, each flask has an

identical pressure, volume, and temp.

• Which flask contains the most atoms?

• Which flask has the highest mass density?

• If the He is heated and the Ar cooled, and

the Ne left the same:

– Which will have the highest pressure?

– Which Will have the most moles?

– Which will have the highest mass density?

Partial Pressure sum of the parts is equal to the whole

Atmospheric Composition – Earth (mole fraction)

Total P = 1.013 bar

N2: 78.08%

O2: 20.95%

Ar: 0.93%

CO2: 0.04%

Other: Trace

Atmospheric Composition – Venus (mole fraction)

Total P = 92 bar

What is the total pressure once the

valve is opened?

A sealed 3.5 L flask contains SO2 gas at a

pressure of 425 torr and O2 gas at a pressure of

650 torr. The two react to produce SO3 at a

constant temperature of 220oC.

What is the partial pressure of SO3 AND the

total pressure inside the flask after the reaction

is complete?

• The molar mass of a gas can be determined through

measurements of its vapor density. In one experiment,

5.22 g of a volatile liquid is added to a 200.0 mL flask

with a narrow opening. The flask is submerged in boiling

water and the liquid inside is allowed to evaporate. The

outside pressure is 752 Torr. After the liquid has

evaporated the flask is capped, cooled and reweighed.

The vapor condenses and the mass of the condensed

liquid is determined to be 0.388 g.

– What is the molar mass of the liquid?

• The compound is found through other experiments to be

40.0 % by mass carbon, 53.3 % oxygen and 6.7 %

hydrogen.

– What is the formula of the compound?

Kinetic-Molecular Theory

Kinetic Energy = ½ (mass)*(velocity)2

How fast do the children have to be going to

match the kinetic energy of the Mack the truck?

½ mT*vT2 = ½ mC*vC

2

½*300mC*vT2 = ½ mC*vC

2

300vT2 = vC

2

Temperature = average energy of system

Two samples of gas have the same volume, pressure, temperature, and moles

One is Helium, the other is Xenon:

• Which one will have a higher mass density?

• Which one have a higher energy?

• Which one will have a higher average gas particle velocity?

30,000 lbs

100 lbs V1

V2

Postulates of the Kinetic-Molecular Theory

Because the volume of an individual gas particle is so

small compared to the volume of its container, the gas

particles are considered to have mass, but no volume.

Gas particles are in constant, random, straight-line

motion except when they collide with each other or with

the container walls.

Collisions are elastic therefore the total kinetic energy(Kk) of the

particles is constant.

Postulate 1: Particle Volume

Postulate 2: Particle Motion

Postulate 3: Particle Collisions

Postulate 4: No attractive forces/interactions

Molecules do not attract each other or interact with each other.

A glass bottle is filled with Helium gas at room

temperature and sealed. If the glass bottle is

submerged in liquid nitrogen…

• What will happen to the pressure of the

gas inside the bottle?

• Why? – A result of the helium atoms remaining at a constant

pressure while in a sealed enclosure

– The frequency of collisions between gas particles and

the glass wall decreases

– Force of collisions of helium atoms with container

decreases with temperature

– Helium atoms occupy smaller volume in colder temps

– The gas density of the Helium decreases with

temperature

Figure 5.14 Distribution of molecular speeds at

three temperatures.

Figure 5.19 Relationship between molar mass and

molecular speed.

The heavier the particle, the slower average

speed in the population (at a given temperature)

5 | 34

• Effusion

• The process by which a gas flows through

a small hole in a container. A pinprick in a

balloon is one example of effusion.