a summary of terminology for oxidation- reduction …...figure 4.12 a summary of terminology for...
TRANSCRIPT
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)
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• 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.