Representative Gases & Properties of
Gases
1. State the five assumptions of the Kinetic-Molecular Theory of gases.
a) Gases consist of large numbers of tiny particles. These particles, usually
molecules or atoms, typically occupy a volume about 1000 times larger than
occupied by the same number of particles in the liquid or solid state. Thus
molecules of gases are much further apart than those of liquids or solids.
Most of the volume occupied by a gas is empty space. This accounts for the lower
density of gases compared to liquids and solids, and the fact that gases are
easily compressible.
b) The particles of a gas are in constant motion, moving rapidly in straight
lines in all directions, and thus passes kinetic energy. The kinetic energy of
particles overcomes the attractive forces between them except near the
temperature at which the gas condenses and becomes a liquid. Gas particles
travel in random directions at high speeds.
c) The collisions between particles of a gas and between particles and container
walls are elastic collisions. An elastic collision is one in which there is no
net loss of kinetic energy. Kinetic energy is transferred between two particles
during collisions, but the total kinetic energy of the two particles remains the
same, at constant temperature and volume.
d) There are no forces of attraction or repulsion between the particles of a
gas. You can think of ideal gas molecules as behaving like small billiard balls.
They move very fast, and when they collide they do not stick together, but
immediately bounce apart.
e) The average kinetic energy of the particles of a gas is directly proportional
to the Kelvin temperature of the gas. The kinetic energy of a particle (or any
other moving object) is given by the equation: KE = 1/2mv2. Where m is the mass
of the particle and v is the velocity.
2. List the five properties of gases (add the extra one too!)
a) Expansion Gases do not have a definite shape of definite volume. They fill
the entire volume of an container in which they are enclosed and assume its
shape. A gas transferred from 1-L to a 2-L vessel will quickly expand to fill
the entire 2-L volume.
b) Fluidity Because the attractive forces between gas particles are negligible,
gas particles glide easily past one another. This ability to flow causes gases
to show mechanical behavior similar to that of liquids. Because liquids and
gases flow, they are referred to collectively as fluids.
c) Low density The density of a substance in the gaseous state is about 1/1000
the density of the same substance in the liquid or solid state because the
particles are so much farther apart in the gaseous state. For example, oxygen
gas has a density of .001 g/mL, at 0°C and 1 atmosphere pressure. As
liquid at -183°C, oxygen has a density of 1.149 g/mL.
d) Compressibility During the compression of a gas, the gas particles which are
initially very far apart, are crowded closer together. Under sufficient
compression, the volume of a given sample of gas can be decreased thousands of
times. The steel cylinders containing nitrogen, oxygen, or other gases under
pressure that are widely used in industry illustrate this point. Such cylinders
have internal volume of about 55 L. When they returned "empty" at
ordinary pressures, they contain about 55 L of gas, although when they were
delivered "full" they may have had 100 times as many molecules of gas
compressed within the same cylinder.
e) Diffusion Gases spread out and mix with one another without stirring and in
the absence of circulating currents. If the stopper is removed from a container
of ammonia, the presence of this gas, which irritates the eyes, nose, and
throat, soon becomes evident. Eventually, the ammonia mixes uniformly with the
air in the room, as the random and continuous motion of the ammonia molecules
carries them throughout the available space. The spontaneous mixing of the
particles of two substances because of their random motion is referred to as
diffusion.
f) Exertion Gases also have the ability to exert pressure on a surface.
3. Methods of production of the representative gases.
1) Balanced equations required:
a) Oxygen (2 methods): One method of preparation is decomposing hydrogen
peroxide. Oxygen can be
prepared by passing hydrogen peroxide through a catalyst, manganese dioxide. It
is then collected by
water displacement. The second method is decomposing water through electrolysis.
Electricity is passes
though water, separating Hydrogen and Oxygen. Method 1: 2H2O2(aq) -MnO2ą
2H2O(l) + O2(g).
Method 2: 2H2O(l) -electrical energyą 2H2(g) + O2(g).
b) Ozone (1 method): If enough energy is present, O2 will become O3. Method:
3O2(g) + energy ą 2O3(g).
c) Hydrogen (2 methods): One of the methods of preparing Hydrogen is just like
preparing Oxygen, through the use of electrolysis.
Method 1: Method 2: 2H2O(l) -electrical energyą 2H2(g) + O2(g). Another
commonly used method is reacting metals with acids. Method
2: Zn(s) + H2SO4(aq) ą ZnSO4(aq) + H2(g).
d) Ammonia (1 method): The Haber Process is the catalytic systhesis of ammonia
from nitrogen gas and
hydrogen gas. Method: N2(g) + 3H2(g) ßcatalystą 2NH3(g).
2) Description of method required:
a) Carbon Dioxide: Carbon dioxide is usually produced when combustion of carbon
compounds occur, decompose carbonates, and aerobic respiration.
b) Carbon Monoxide: Carbon Monoxide is commonly produced when incomplete
combustion occurs. Most carbon monoxide comes from the exhuast of cars.
c) Nitrogen: In labortories, Nitrogen is produced by heating certain compounds
that contain ammonia.
4. List the physical and chemical properties of gases in SQ 8.
Oxygen: Physical - Oxygen is a gas that is odorless, colorless, tasteless, and
is denser than air. It appears to be a pale blue color when in liquid and solid
states. Chemical - Very electronegative and tends to form oxides and peroxides.
Ozone: Physical - Ozone is a gas that is pungent, pale blue in color, and tastes
bitter. Its Lewis Dot structure is resonance.
Nitrogen: Physical - Nitrogen is a gas that is odorless, colorless, tasteless,
and less dense than air.
The liquid states is commonly used for freezing involving medical purposes. It
appears white in its solid form.
Chemical - Because of its triple bond, nitrogen is not very reactive. It tends
to react with hydrocarbons to form photochemical smog.
Ammonia: Physical - Ammonis is a gas that is strong and pungent, it is
colorless, and tastes bitter.
Carbon Dioxide: Physical - Carbon Dioxide is a gas that is distinct in scent,
colorless, and tastes sour. It s denser than air and its Lewis Structure is
resonance. Chemical - Extremely stable, absolutely does not support combustion.
Carbon Monoxide: Physical/Chemical - Carbon Monoxide is a gas that is very toxic
and almost impossible to tell if it is present. Hemoglobin is also 300 times
more sesceptible to Carbon Monoxide than Oxygen.
Hydrogen: Physical - Hydrogen is a gas that is odorless, colorless, tasteless,
and less dense than air.
It is clear in both liquid and solid states, it appears to be ice-like in its
solid state. Chemical - Hydrgen is highly reactive. It basically reactes with
anyting around it. Mostly in existance with compounds involving non-metals.
5. Know some of the uses of the gases in SQ8.
Oxygen: Commonly used in aerobic respiration and combustion. Nitrogen: Commonly
used to freeze things for medical purposes, cooling, and propellant for aerosol
products, also used to prolong life of food products.
Carbon Dioxide: Commonly used in baking to make dough rise, used for freezing,
plants use it for producing glucose, and fire extinguishers.
Hydrogen: Commonly used for hydrogenation and fuel.
6. A colorless, odorless and tasteless gas is found. What are some of the
tests and retults which can be used to identify the gas? Which gases can be
eliminated based on odor? Color? Which gas is most difficult to identify?
Possibilities for colorless odorless and tasteless gas: Oxygen, Nitrogen, Carbon
Monoxide, and Hydrogen.
If Oxygen was in a test tube and you placed a buring splint up to it, it should
suck the flame in and make a "pop" sound. Or it would re-ignite a
glowing splint. oOnly Oxygen and Ozone have color in their liquid and solid
states. oOnly Carbon Dioxide, Ozone, and Ammonia have odor.
The most difficult gas to identigy would be Hydrogen.
7. Define allotrope
Allotrope - One of the two or more forms of an element that exists in the same
physical state.
8. What is a eudiometer?
Eudiometer - A eudiometer is a gas collecting tube.
9. What kinds of attractive forces exists between molecules? Describe all
three. How are these attractive forces different from those we stuidied
previously?
Intermolecular forces - The forces of attraction between molecules.
Dipole-dipole forces - The forces of attraction between polar molecules.
London dispersion forces - Intermolecular attractions resulting from the
constant motion of electrons and the creation of intantaneous dipoles and
induced dipoles.
10. What is an ideal gas? When does a real gas behave like an ideal gas?
An ideal gas is a gas that fits the kinetic molecular theory perfectly.
Noble gases tend to behave like an ideal gas. Real gases behave like an ideal
gas when it fits the 5 assumptions of KMT.