Unit 2 of Physics and Chemistry for 3rd year of ESO

1. THE STATES OF MATTER

2. Remembering
magnitudes and units
In this unit we'll use these units, you must learn them by heart
MAGNITUDE UNIT SI Remember
Kg
MASS 1 Kg = 1000 g
(kilograme)
1 m3 = 1000 L
VOLUME m3 1 L = 1000 mL
(cubic meter) 1 L = d m3
1 cm3= 1 mL
Pascal 1 atm = 101300 Pa
PRESSURE
(Pa = N/m2) 1 atm = 760 mm Hg
K
TEMPERATURE T( K ) = T (º C) + 273
(Kelvin)

3. Properties of matter
● Matter has two kinds of properties:
– General properties: they are common to all
kinds of matter:
● mass, volume, temperature,...
– Specific properties: they are different for
every kind of matter:
● Melting temperature, boiling temperature,
density, electric conductivity,...

4. Macroscopic behaviour
Macroscopic properties of solids, liquids and gasses.
SOLID LIQUID GAS
It has its own shape It adapts to the shape of its container
It is not easily compressible It is easily compressible.
It doesn't flow It flows It flows
It tends to fill all aviable
space
It has its own volume It has its own volume
Any two gasses are mixed
easily

5. Kinetic Theory
● The kinetic theory explains the behaviour
of solids, liquids and gasses.
● It's based on three ideas:
– Matter is made of particles
– The particles are in continuous motion:
● Temperature is a measurement of the
average kinetic energy of the particles.
● If the system is hotter, its particles move
faster
– All particles attract each other with a force.

6. Kinetic Theory
MICROSCOPIC BEHAVIOR OF THE DIFFERENT STATES
SOLID LIQUID GAS
The only possible Every particle can Every particle has a
Particles' motion movement is slide over its uniform rectilinear
vibration neighbours motion
Every particle is in Every particle is in The distance is much
Distance between
contact with its contact with its bigger than particle's
particules
neighbours neighbours size
There are almost no
Atractive force
Very strong forces Weak forces forces between
between particules
particles

7. Kinetic Theory

8. Kinetic Theory and solids
● These questions about solids can be
answered using the kinetic theory:
– Why do solids keep their own shape?
– Why do solids increase their volume when
they are heated?
– Why do solids became liquids when their
temperature increase enough?
– Why can't solids be compressed?

9. Kinetic Theory and liquids
● These questions about liquids can be
answered using the kinetic theory.
– Why can they flow?
– Why can't they be compressed?
– Why do liquids increase their volume when
they are heated?

10. Kinetic Theory and gasses
● The temperature is related to
the average kinetic energy of
the particles of a system.
– If the temperature raises, the
particles move faster.
● Gasses exert pressure on the
container walls:
– Pressure is a consequence of
the collision of particles
with the container walls.

11. Kinetic Theory and gasses
● A few questions that we can answer with the
kinetic theory (I):
– Any two gasses can be mixed together.
Why?
– Why can gasses be compressed easily?
– Why can gasses flow?
– ...

12. Kinetic Theory and gasses
● A few questions that we can answer with the
kinetic theory (II):
– ...
– Does pressure change when a gasses is
heated? How? Why?
– Does pressure change when we reduce the
volume of the container of a gas? How?
Why?
– Why do gasses tend to fill all available
space?

13. Gasses' Laws
● Charles' Law: describes how gasses
expand when heated.
● At a constant pressure, the volume of a gas
increases or decreases proportionally to
its absolute temperature.
– Don't forget: T(K) = t(ºC) + 273
V
= constante
T
V1 V2
=
T1 T2

14. Gasses' Laws
● Charles' Law
● Use the Internet for more
information:
● Practise doing numeric
exercises about this law:
http://www.educaplus.org/gases/e
● A simple experiment about
Charles' Law
http://youtu.be/ATje2S5YZNo
● An interactive on-line
software about Charles' Law
http://www.educaplus.org/gases/fl

15. Gasses' Laws
● Gay-Lussac's Law: describes the relationship
between pressure and temperature in gasses
contained in rigid containers (V = constant)
● At a constant volume, the pressure of a gas
increases or decreases proportionally to its
absolute temperature. Don't forget: T(K) = t(ºC) + 273
p
= constant
T
p1 p2
=
T1 T2

16. Gasses' Laws
● Gay-Lussac's Law
● Use the internet for more
information:
● Practise doing numeric
exercises about this law:
http://www.educaplus.org/gases/e
● A simple experiment about
Gay-Lussac's law:
http://youtu.be/VNU6YpKmLtM

17. Gasses' Laws
● Boyle-Mariote's Law: describes how gasses
are compressed.
● At a constant temperature, the pressure and
the volume of a gas are inversely
proportional.
p · V = constant
p1 · V 1 = p 2 · V 2

18. Gasses' Laws
● Boyle's Law
● Use the internet for more
information:
● Interactive on-line software
about this law:
http://www.educaplus.org/gases/fl
● A experience about this law:
http://youtu.be/J_I8Y-i4Axc
● Practice doing exercises
about this law:
http://www.educaplus.org/gases/e

19. Gas Equation
● The three laws we saw before can be
reduced to an only equation: the gas
equation
● We must use it if p, T and V change at the
same time. Be careful: T must be expressed en Kelvin
p·V
= constant
T
p1 · V 1 p 2 · V 2
=
T1 T2

20. Changes of State
● All matter can move from one state to
another.

21. Changes of state
● Sometimes matter absorbs energy when its state
changes (progressive changes of state)
– (Graph: from left to right)
● In other occasions, matter gives off energy (regressive
changes of state)
– (Graph: from right to left)

22. Changes of state.
How Kinetic Theory explains them
● When a solid is heated
up its particles move
faster.
● The forces between
particles can't keep
them vibrating around
fixed positions.
● The particles can now
See in the internet
slide past one other.
● The solid becomes a
liquid.

23. Changes of state.
How Kinetic Theory explains them
● When a liquid is heated
its particles move
faster.
● The forces between
particles can't keep
themselves together.
● The particles can now
separate each other.
See in the internet
● The liquid becomes a
gas.

24. Changes of state.
Evaporation and boiling
● Vaporisation can happen in two different
ways. There are two ways of changing liquid
into a gas:
– Evaporation: the particles that are the
nearest the surface are weaklier united to
its nearby particles. They can separate
from the others more easily.
– Boiling: if the motion of particles is fast
enough, all particles can separate from
each other.

25. Changes of state.
Evaporation and boiling
● There are two main differences between both
of them:
– Evaporation occurs only in the surface of
the liquid and boiling takes place in
inside the liquid (bubbles of gas appear
and go up to the surface of the liquid).
– Boiling happens at a specific temperature
(boiling point), there are not a specific
temperature for evaporation

26. Changes of state
Heating curve
● When we heat a solid, its
temperature changes with
time as we can see in the
graph
● The temperature keeps
constant during every
change of state.
● Tf: melting point: The
system can be solid, liquid or
a mixture of both.
● Te: boiling point: The
system can be liquid, gas or
a mixture of both.

27. Changes of state
Cooling curve
● When we cool a gas, T
keeps constant at boiling
and melting points.
● Tf: melting point:
– The system can be
solid, liquid or a
mixture of both.
● Te: boiling point:
– The system can be
liquid, gas or a
mixture of both.