1.

States of matter
Revision notes
Matter: Matter is any substance that has mass and
occupies space. E.g. wood, iron rod,…etc
• Feelings &senses are not matter. E.g. love, hate, pain,
cool &hot…
• There are three states of matter namely solid, liquid and
gas.
 Properties of solids, liquids and gases
Solids Liquids Gases
• particles have a • particles have a • particles have a
regular arrangement random arrangement random arrangement
and are close and are close and are spread apart
together together •have no fixed shape
• have a fixed volume • have a fixed volume or volume, Take the
and a fixed shape but no fixed shape, shape of their
• Strong forces of Take the shape of container
attraction their container •Almost no
Between particles •Weaker attractive intermolecular forces
•Can’t be forces than solids •Can be compressed
compressed • moderate •Particles widely
•Particles vibrate compressed spaced in random
around a fixed point •Particles move order
random/freely •Particles moving
Structure of solids, liquids and gases in terms of particle separation arrangement and
types of motion:

• Solid has regular arrangement& least energy – particles

are not moving/are just vibrating & separation by
touching.

• Liquid: particles have random arrangement and are close

together &more energy than those in a solid, but less
than those in a gas. separation is not by touching.

• Gas: particles have random arrangement and are spread

apart & they have most energy – shown by the diagram,
as the particles are the most spread apart, motion is
more random and frequent. separation is not by
touching.
Changes of state
 • Evaporation : happens at the surface, molecules have enough energy to
evaporate – i.e. go from liquid to gas
• Freezing : liquid to solid
• Melting : solid to liquid
• Boiling: happens throughout the liquid, liquid to gas
• Condensation : gas to liquid
• Sublimation : solid to gas or gas to solid
Differences between Evaporation& Boiling :

Evaporation Boiling
•Occurs at only top of the •Occurs at throughout the
liquid liquid
•Occurs at all •Occurs only at fixed
temperature temperature
•Slow process •Rapid process
•Cooling •Heating
Melting
• Melting is when a solid changes into a liquid.
• Requires heat energy which transforms into kinetic energy, allowing the
particles to move.
• Occurs at a specific temperature known as the melting point (m.p.) which
is unique to each pure solid.
Boiling
• Boiling is when a liquid changes into a gas.
• Requires heat which causes bubbles of gas to form below the surface of a
liquid, allowing for liquid particles to escape from the surface and within the
liquid.
• Occurs at a specific temperature known as the boiling point (b.p.) which
is unique to each pure liquid.
 The presence of impurities in a pure substance can change its melting point
and boiling point (m.p. & b.p.).
 Different pure substances can be identified by analysis of the value of their
m.p. or b.p. since this is a physical property which is unique to each substance.
Freezing
• Freezing is when a liquid changes into a solid.
• This is the reverse of melting and occurs at exactly
the same temperature as melting, hence the melting point
and freezing point of a pure substance are the same. Water
for example freezes and melts at 0ºC.
• Requires a significant decrease in temperature (or loss of
thermal energy) and occurs at a specific temperature which
is unique for each pure substance.
Evaporation
• When a liquid changes into a gas. Evaporation occurs only at
the surface of liquids where high energy particles can
escape from the liquid’s surface at low temperatures, below
the b.p. of the liquid.
• The larger the surface area and the warmer the
liquid/surface, the more quickly a liquid can evaporate
• No heat is required and evaporation occurs over a range of
temperatures.
Condensation
• When a gas changes into a liquid, usually on cooling. When a gas
is cooled its particles lose energy and when they bump into each
other, they lack energy to bounce away again, instead grouping
together to form a liquid.
• No energy is required for condensation to occur and it takes place
over a range of temperatures.
Sublimation
• When a solid changes directly into a gas.
• This happens to only a few solids such as iodine or solid carbon
dioxide.
• The reverse reaction also happens and is also called sublimation
(sometimes called deposition or desublimation).
• Sublimation occurs at a specific temperature which is unique for
a pure substance.
Note
• Liquid turns into a gas very easily at room temperature is known as
volatile.

Examles:
1. Bromine liquid turns into a gas very easily at room temperature
2. Many organic compounds are volatile. For example, alcohol is
volatile.
 Predicting a physical state
• The state of a substance at a given temperature can be
predicted if its melting point and boiling point are
known.
• The table summarises how to work this out.

Comparison Predicted state

Given temperature < melting point Solid

/ Below M.P.

Given temperature is between melting Liquid

and boiling points

Given temperature > boiling point Gas

/above B.P.
Effects of temperature and pressure on the volume of a gas

• Heat must be supplied to a substance for it to

melt, evaporate or boil. For example, you need to heat
ice to melt it, and you need to heat water to make steam.
• Heat must be removed from a substance to condense or
freeze it. In other words, the substance must be cooled
down.
• Under certain conditions, some solids turn straight into
a gas when heated. This process is called sublimation.
• A good example is solid carbon dioxide, also called ‘dry
ice’. At atmospheric pressure, it turns straight into
gaseous carbon dioxide.
[Liquid carbon dioxide can only exist under high pressure,
such as in fire extinguishers.]
• Iodine also sublimes - it turns directly from shiny
purple-black crystals to a purple vapour when warmed
up.
Changing the pressure:
• A gas will also liquefy (turn into a liquid) if its pressure is
increased enough. This is because the particles are
moved close enough for bonds to form between the
particles.
• Gas cylinders used for camping stoves and barbecues
contain liquefied petroleum gas (LPG) under high
pressure. As soon as the pressure is released, the liquid
turns back to a gas.
https://www.bbc.co.uk/bitesize/guides/zthyj6f/revision/1
Cooling Curve:

freezing point & Y is the condensing point

• https://phet.colorado.edu/sims/html/states-of-matter-
basics/latest/states-of-matter-basics_en.html
• https://edu.rsc.org/resources/melting-and-freezing-stearic-
acid/1747.article
 Brownian motion
• Particles in liquids and gases (known as fluids) move randomly
this is called Brownian motion.

• This happens because they collide with other moving particles in

the fluid.
• This is evidence for the kinetic particle model of matter- it shows
that there are individual particles which make up
solids/liquids/gases
• Particles in liquids and gases move randomly because they are
bombarded by the other moving particles in the fluid. Larger
particles can be moved by light, fast-moving molecules have light
weight.
Evidence for Brownian motion:
• Robert Brown observed the random movement of
pollen grains within water, which showed that there
were separate particles within the water that were
moving randomly and caused the grain to move
(kinetic theory)
• When you observe smoke particles under a
microscope. They will move around randomly caused
by their collisions with smaller unobservable particles.
In terms of kinetic particle theory, the effects of temperature and
pressure on the volume of a gas
Solids
• In the solid, the particles are touching, and the only motion
allowed to them is vibration. The particles may be arranged
regularly

Liquids
• In a liquid, the particles are mainly touching, but some gaps
have appeared in the structure. These gaps allow the
particles to move, and so the particles are arranged
randomly.

Gases

• In a gas, the particles are entirely free to move. At ordinary

pressures, the distance between individual particles is of the
order of ten times the diameter of the particles. At that
distance, any attractions between the particles are fairly
negligible at ordinary temperatures and pressures.
Melting and freezing
• If energy is supplied by heating a solid, the heat energy
causes stronger vibrations until the particles eventually
have enough energy to break away from the solid
arrangement to form a liquid.
Boiling and condensing
• If more heat energy is supplied, the particles eventually
move fast enough to break all the attractions between
them, and the liquid boils.
A beaker with
elemental iodine (I2)
is heated gently. Solid
iodine sublimates and
then gaseous iodine
condenses on the
walls of the beaker as
well as on the bottom
of a round container
that is kept cold with
some ice inside of it.
• https://www.tec-science.com/wp-content/uploads/2019/03/en-
temperature-kinetic-theory-of-gases-pressure.mp4
• https://www.sciencesource.com/archive/Iodine-Sublimation-and-
Condensation-SS21318336.html
• https://youtu.be/bxaPf7HRjZo
• http://cosmobiologist.blogspot.com/2016/02/sulfur-in-yellows-reds-
and-blues-oh-my.html
• The higher the temperature, the higher the average energy.
The evaporation of a liquid in a closed container
• Now imagine what happens if the liquid is in a closed
container. Common sense tells you that water in a
sealed bottle doesn't seem to evaporate - or at least,
it doesn't disappear over time.
• But there is constant evaporation from the surface.
Particles continue to break away from the surface of
the liquid - but this time they are trapped in the space
above the liquid.
• As the gaseous particles bounce around, some of them
will hit the surface of the liquid again, and be trapped
there. There will rapidly be an equilibrium set up in
which the number of particles leaving the surface is
exactly balanced by the number rejoining it.
• In this equilibrium, there will be a fixed number of the
gaseous particles in the space above the liquid.
Q
 Diffusion
• Diffusion is the movement of particles from higher
concentration to lower concentration area.
• The rate of diffusion is higher when temperature Is
more as the particles at higher temperature have more
kinetic energy thus they move at a greater speed.
• The rate of diffusion also depends upon the molecular
mass of the particle, the lighter the particle the faster it
diffuses.
Factors affecting the Rate of Diffusion:
• Temperature: As temperature increases, the rate of
diffusion increases. This occurs as particles at higher
temperature have higher kinetic energy and thus are
able to move at higher speed from region of higher
concentration to less concentration.
• Molecular Mass of the particle: Particles having less
mass have higher rate of diffusion than those which
have greater mass considering that the temperature
remains constant. Therefore gases having lower
density have greater rate of diffusion.
• https://phet.colorado.edu/sims/html/diffusion/latest/diffusion_en.ht
ml
• https://examples.yourdictionary.com/examples-of-diffusion.html
• https://edu.rsc.org/resources/diffusion-of-gases-a-safer-alternative-
to-bromine/684.article
• https://edu.rsc.org/resources/diffusion-of-gases-ammonia-and-
hydrogen-chloride/682.article
• https://edu.rsc.org/resources/diffusion-in-liquids/685.article
(a) (i) (particles) spread to fill total available volume /
move from high concentration to low concentration /
moves down a concentration gradient (1)
[1]
(ii) mass or Mr (1) [1]
(b) (i) helium atoms / molecules are lighter than
molecules in air or N2 and O2 or helium is less dense
than air or N2 and O2. or helium diffuses (through the
porous barrier) faster than air or N2 and O2. (1)
[1]
• (ii) faster rate of diffusion / molecules move faster (at
high temperatures). (1) [1]