Characteristics of Gases
1. Expansion –
Gases have neither definite shape nor volume but expand to fill any container.
2. Fluid –
Particles flow or glide past each other.
3. Low Density
– Gas particles are far apart and so have a low mass to volume ratio (since their volume is large compared to
- Gas particles can be moved closer together (since they are far apart).
A pressurized container can be made to hold up to 100X more particles than a non-pressurized container would.
– Movement of gas particles from an area of greater to one of lesser concentration until a dynamic equilibrium is
Diffusion depends on 1. The speed of the gas particles, 2. The size of the gas particles and 3. The attractive forces between
– The process by which gas particles pass through a small opening.
This depends on the speed of the particles.
Kinetic Molecular Theory of Matter =
A theory that explains how
particles in any state of matter are in constant motion.
Kinetic Molecular Theory of Gases (KMT) =
A theory that provides a model of an ideal gas.
= An imaginary gas that perfectly fits all the assumptions of this theory.
There is no such thing as an ideal gas although the noble gases show ideal behavior over a wide range of temperature and
pressure since their particles are monatomic and nonpolar.
Polar gases deviate from ideal behavior.
Ideal-like conditions for a gas are low pressure and high temperature.
= A gas that does NOT behave according to the assumptions of the KMT.
Assumptions of KMT:
Gases consist of a large number of small particles that are very far apart.
So a gas is mostly empty space.
There are NO forces of attraction or repulsion between gas particles.
Gas particles are in continuous, rapid, random motion and so possess kinetic energy.
Kinetic Energy (KE)
= The energy of motion.
Collisions between gas particles and between particles and the walls of the container are elastic.
A collision in which there is no net loss of KE as heat due to friction.
(ie. KE is transferred but not lost)
The average KE of gas particles depends on the absolute
(Kelvin) temperature(T) of the gas.
- This is the equation for KE:
KE = ½ mv
where m is the mass of the particle and v is the velocity or speed of the particle
All gases at the same T have the same KE so the lighter the gas particle is, its speed will be higher/faster than a heavier
To fully describe a gas you need to include the following, because gases vary as these conditions vary:
number of molecules
A force per unit area exerted on a surface.
Pressure = force/area.
SI unit is the Newton/meter
or the Pascal(Pa)
A device used to measure atmospheric pressure.