The Particle and Kinetic Theory of Matter
Phenomena which led scientists to believe that matter is made up of particles:
1.
2.
3.
The theory is based on 3 assumptions:
1.
2.
3.
Matter is made up of tiny particles (atoms, ions or molecules)
Particles of Matter are in constant and random motion.
The higher the temperature, the faster the speed of the particles.
Temperature
Temperature is a measure of the average kinetic energy of the molecules (particles) in a
system.
(kinetic energy is energy due to the motion of molecules)
Therefore the coldest possible temperature is when the molecules in a system are
not moving at all. This happens at -273 oC. (ABSOLUTE ZERO)
Kelvin Scale
This temperature scale uses divisions which are the same as the Celsius scale but instead of
zero being the temperature of melting ice (0 oC) it is instead the coldest possible temperature
– Absolute Zero (0 K)
Celcius Scale oC
-273
0
100
Therefore:
C  K add 273
o
Kelvin Scale K
0
273
373
K  oC subtract 273
Convert the following:
47 oC
84 K
586 K
-167 oC
1128 oC
PHASES OF MATTER
All matter can be placed in one of three phases; solid, liquid gas. What phase are the
following at room temperature?
a) water
b) nitrogen
Phases:
SOLID
c) glass
d) tin
LIQUID
GAS
Flow easily to take
the shape of the
container
Takes the volume
of container
Low
Can be compressed
into a much smaller
volume
Shape
Fixed shape
Volume
Constant volume
Flow easily to take
the shape of the
container
Constant volume
Density
Compressibility
High
Cannot be
compressed into a
smaller volume
Medium
Some can be
compressed by tiny
amounts.
The particle model of matter helps to explain many of the different
properties of matter.
1.
Phases of matter
SOLID
Arrangement
of particles
Forces
between
particles
Diagram
LIQUID
GAS
Particles are tightly
packed in a fixed
pattern.
Particles are still in
contact but are slightly
further apart than in a
solid and have no fixed
pattern.
Particles are very far apart
and have no fixed pattern.
Particles make tiny
vibrations about a
fixed position.
Particles are free to
slide past each other.
Particles move freely
throughout the container.
Strong forces.
Weaker forces than in a
solid.
Very weak forces (almost no
forces at all)
2.
Phase changes
Condensation
Boiling or evaporation
When a substance is heated the particles get more energy and move faster until they have
enough energy to overcome the forces holding them together and the substance then
undergoes a change of phase, eg solid to liquid or liquid to gas.
e.g. Melting:- When a solid is heated the molecules move faster. At the melting point the
molecules break from their fixed positions and begin to slide over one another
and a liquid is formed.
e.g Boiling:- _______________________________________________________________
_______________________________________________________________
_______________________________________________________________
Examples of substances which sublime are dry ice (solid carbon dioxide) and iodine.
Why is dry ice so useful? ______________________________________________________
___________________________________________________________________________
When solid iodine is heated the black solid sublimes to form a ......................................... gas.
LATENT HEAT (“Hidden” heat at phase changes)
When a phase change is happening (e.g melting) the temperature
stays more or less constant despite the fact that energy is being
added or removed from the system. This energy is called “latent
heat” because it seems to disappear.
This release of energy as steam condenses is why a scald from steam can cause such a terrible
wound. All the energy released damages the skin and flesh below. Steam is therefore very
dangerous. Be careful when lifting the lid from a pot or kettle or (especially) microwave
container.
THE EFFECT OF IMPURITIES ON MELTING AND BOILING POINT OF A
SUBSTANCE
Melting points: These DROP. E.g when salt is added to ice it melts (and its temperature
drops). This is used to remove ice from roads in some
countries.
Boiling points: These RISE.
E.g. salt water (103 oC) has a higher boiling point than fresh
water
Boiling points are also affected by pressure. The higher the pressure the higher the boiling
point.
e.g.1 Water boils at lower temperature the higher the altitude. The boiling point on top of
Mount Everest is only 70 oC.
e.g.2 How does a pressure cooker work?
__________________________________________________________________________
__________________________________________________________________________
Evaporation
This is the loss of molecules through the
surface of a liquid into the gaseous phase.
It is the faster moving molecules which leave
a liquid. Therefore the molecules left are
moving slower on average and the liquid
cools.
A liquid which evaporates readily is called
VOLATILE. (e.g. ether)
List 4 factors which increase the rate of evaporation of a liquid like water.
1.
__________________________________________________________________
2.
__________________________________________________________________
3.
__________________________________________________________________
4.
__________________________________________________________________
3.
BROWNIAN MOTION
Robert Brown noticed that pollen grains on water were seen to be
moving in a random way when observed under a microscope. He
concluded that invisible tiny particles were moving very fast and were
colliding with the pollen grains causing them to move in a haphazard
way.
The above observation provides some evidence for the kinetic theory.
Note: smoke in air produces the same effect. In it little ash particles are seen to move as
the air molecules bash into them.
4.
DIFFUSION
This is the spreading of one substance into another.
Liquids and gasses diffuse – solids do not.
When a gas jar containing air (colourless) is placed on top of a gas jar containing a redbrown gas (e.g. nitrogen dioxide or bromine), the red-brown colour spreads up into the air
until the gas in both jars looks the same colour.
Gases diffuse faster than liquids. Explain why.
________________________________________________________________________
________________________________________________________________________
Hot gases diffuse faster than cool ones. Explain why.
________________________________________________________________________
________________________________________________________________________
Heavy gas molecules diffuse more slowly than light ones. Explain why.
________________________________________________________________________
________________________________________________________________________
e.g. Hydrogen chloride (HCl) molecules diffuse slower than ammonia (NH3).
HCl
Ammonium chloride
NH3
5.
PRESSURE OF GASES
The pressure of a gas results from molecules colliding with the sides of the container.
Therefore the greater the number of collisions and the greater the average force of the
collisions, the greater the pressure.
a)
Pressure and volume.
If the volume of a fixed mass of gas is decreased the pressure increases.
Explain why this happens in terms of collisions.
___________________________________________________________________
___________________________________________________________________
pressure
volume
b) Pressure and temperature.
If the temperature of a fixed mass of gas is increased then its pressure will increase.
Explain why this happens in terms of collisions.
___________________________________________________________________
___________________________________________________________________
pressure
Temperature (K)