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) ExpansionGases 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) FluidityBecause 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 densityThe 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 0C and 1 atmosphere pressure. As
liquid at -183C, oxygen has a density of 1.149 g/mL.
d) CompressibilityDuring 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) DiffusionGases 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) ExertionGases 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) -MnO2 2H2O(l) + O2(g).
Method 2: 2H2O(l) -electrical energy 2H2(g) + O2(g).
b) Ozone (1 method): If enough energy is present, O2 will become O3.Method:
3O2(g) + energy2O3(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 energy 2H2(g) + O2(g). Another commonly used method is
reacting metals with acids.Method
2: Zn(s) + H2SO4(aq) 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) catalyst 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
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.
oIf 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.