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Bonding, structures of crystalline substances and energy changes (Energy…
Bonding, structures of crystalline substances and energy changes
Bonding
Covalent bonding
Polar & non-polar
Covalent bonds
non-polar bonds
formed between
2 non-metal atoms
of the
same kind
the shared electron pair is attracted to the nuclei to the same extent for both atoms
....therefore, the
electron cloud formed is symmetrical
the electromagnetically cancels each other out, so it is non-polar
....has
no bond dipole
, because it cancels out
Polar bonds
formed between
2 different kinds
of
non-metal atoms
the shared electron pair is attracted to the
nucleus of one atom more than the other
....therefore, the
electron cloud formed is unsymetrical
one end of the bond has a
slightly greater electromagnetically relative
to the other end
... therefore there is a charge separation
... and a
bond dipole
exists
if the
bond dipoles are opposite directions
= they
cancel each other out
and are
therefor
non-polar
molecules
if there is a
bond dipole
, they
don't cancel out
,
and the molecule is
polar
example answer
for polarity of molecules question:
two polar C-O bonds. O is more electronegative that C,
the polar bonds are arranged in a symmetrical linear shape.
The bond-dipoles cancel each other out, so CO2 is non-polar
Polar bond vs. polar molecule:
polar
bond
:
a
Bond dipole
exists
... as there is a c
harge separation within the bond
... due to
one atom being more electronegative that the other
Polar
molecule
:
a
molecular dipole
exists
... as there is a
charge separation over the whole molecule
... the
bond dipoles within the the molecule don't cancel out
because of the
molecules shape
Atoms
'want' to obtain a full out shell
so they must loose or gain electrons, they do this by Sharing electrons
most atoms need
8 electrons
to have a full out shell
Hydrogen (H) only need 2 electrons
between
2 non-metals
the shared electrons are attracted to
both nuclei simultaneously
Atoms Covalently bonded together = A molecule
when atoms share more than one pair of electrons
= A multiple Covalent bond
=
sharing electrons
to gain a full outer shell
A
bond dipole = a charge separation
at different ends of the bond
(if one molecule is more elctronegative than the other then this creates a bond dipole
(separation of charge)
the
size of the bond dipole
and
degree (angle) of polarity or the bond
= will
differ depending on the atoms involved
Electronegativity
= how well / the
ability an atom has to attract a bonding set of electrons / a shared electron pair
The greater an atom is able to attract the shared electron pair = a more electronegative element
On the periodic table the upper right corner is the most electronegative and the lower left most corner are the least electronegative
polar v.s. non-polar molecules:
Non-polar molecule:
electrons are spread evenly
throughout the molecule
no charge separation
over the molecule
... therefore
no molecular dipole exists
... so the molecule is
overall non-polar
Polar molecule:
electrons are not spread evenly
throughout the molecule
one part/n=bond is more electronegative relative to the other part
there is
charge separation
over the molecule
... therefore a
molecular dipole exists
if the
shape is symmetrical
the
dipole with cancel out
and the molecule will be overall
non-polar
if the shape is
asymetrical
then the
dipole won't cancell out
and overal the molecule will be
polar
the
effects of polar and non- polar molecules:
because
polar molecules have
slightly 'charged' positive & negative part
s...
polar molecules mix with other polar molecules
the molecules are attracted towards each other,
creating a
strong bond
...therefore,
lots of energy is required
to separate
the molecules
... so they have
higher melting/boiling points
Because non-polar molecules
have cancelled out charge
...
the bonds between the molecules are
not strong
... so the molecules are
easily separated
... they have
low melting/ boiling points
water (H2O):
attraction between molecules =
hydrogen bonding
= extremely polar substance
...so molecules are attracted strongly towards each other
to a
create a strong bond
... this means lots of energy is needed to separate the bonds
... so has a high melting/boiling point
water molecules strongly attract other ions
ionic bonds can be overcome by water molecules
.. so many ionic solids can dissolve in water
... they are said to be soluble in water
Polar substances are more reactive
than non-polar substances
Ionic Bonding
the charge must be written on the Lewis structures
=
Exchanging electrons
to gain a full outer shell
Between a
Metal and non-metal
pos
itive ion = have
lost
electrons
neg
ative ions = have
gained
electrons
Lewis structures
Lewis structures can be used to represent
atoms and molecules/compounds and
their valence electrons and
bonds
valence electron pairs are represented as...
non bonding pairs = dashes "-"
bonding pairs = dotes ".."
Each atom 'needs' 8 valence electrons =
4 electron pairs
(except hydrogen,witch only needs 2 valence electrons / one pair)
Steps
to Drawing
Lewis structures:
1)
calculate the total number of
valence electrons in the molecule
(then divide this by 2,
to find the number of electron pairs)
2)
write the symbols for the atoms of the molecules,
in the appropriate position
(the atom with the most incomplete
valence shell goes in the middle)
3)
place the
bonding pairs
of electrons
between the atoms
4)
place the
non- bonding pairs
of electrons
around the atoms
, to fill their out shells (start with the outer atoms)
if there aren't enough for the middle atom then this molecule is said to be electron deficient
5)
if needed; shift non-bonding pairs of electrons to create multiple bonds, and fill the outer shells;
group
17
= only
single
bonds
group
16
=
double or single
bonds
group
15
=
triple, double or single
bonds
the
octane rule
:
almost all atoms need 8 valence electrons
(4 electron pairs)to fill there out shell and therefor be stable,
However....
Hydrogen
(H) = only need
2 electrons
(1 electron pair)
-
Beryllium
(Be) = only needs
4 electrons
(2 electron pairs)
Boron
(B) = only needs
6 electrons
( 3 electron pairs)
the
Octet Rule
= 'All' atoms need 8 electrons in
their valence shell (4 electron pairs)
shapes and
bond angles:
Bond angle:
Depends on...
the total number of electrons density regions
around the central
Bond shape:
Depends on...
Total regions of electron density
weather they are bonding or non-bonding regions
maximum seperation to achieve a state of minimun repulsion
regions of electron dencity repell each other as far aprt as possible
Bond shapes:
the different shapes:
Tetrahedral:
(this is the most common)
4 regions
of electrons around the central atom
lone pairs
of electrons around the central atom
bond angle =
109 degrees
V-shape / Bent:
3 region
s of electrons around the central atom
1 lone pair
of electrons around the central atom
bond angle =
120 degrees
4 regions
of electrons around the central atom
2 lone pairs
of electrons around the central atom
bond angle =
109 degrees
Trigonal Planar:
3 regions
of electrons around the central atom
0 lone pairs
of electrons around the central atom
bond angle =
120 degrees
Trigonal Pyramid:
4 regions
of electrons around the central atom
1 lone pair
of electrons around the central atom
bond angle =
109 degrees
Linear:
2 region
s of electrons around the central atom
0 lone pairs
of electrons around the central atom
bond angle =
180 degrees
when drawing the shape
of a molecule in 3D:
a
circle
(o) = represents the
central atom
in the molecule
a
straight line
(-) = indicates
bonding pairs of electrons
wedge
= indicates the
lone pair of electrons
are coming
forward
(the atom/group is in front of the central atom)
a
dotted line
(----) = indicates the
lone pair of electrons
are going
backwards
(the atom/group is behind the central atom)
steps to determine
the shape:
1)
draw the Lewis structure for the molecule
2)
identify the number of;
regions of electron density around the central atom
number of electron repulsion's around the central atom that are lone pairs
3)
determine and draw this shape based off this information
for both ions and molecules:
single, double, and triple bonds
are all
considered a
single region of electron density
shapes of
Ions:
shapes of ions can be determined
using the same method as for shapes of molecules,
Accept...
the
charge of the ion must be
indicated in the diagram
Symmetrical vs. Asymmetrical shapes:
Asymmetrical shapes:
Bent / V-shape
trigonal planar
(generally these =
polar
molecules )
symmetrical shapes:
linear
trigonal planar
tetrahedral
(generally these =
non-polar
molecules)
(If the the molecule contains lone pairs then it is asymmetrical and therefore likely polar)
Electron clouds = electron density regions
= a single, double or triple
bonding pair of electrons
or lone pair pf electrons
electron clouds:
they're
negatively charged
(because electrons are negatively charged)
are
around the central atom
(in the bond/molecule)
repel each other, to be as
far away from each other as possible
have maximum separation to achieve
minimum repulsion
Formulas for some
common molecules
Pure elements
Hydrogen = H2
Nitrogen = N2
Oxygen = O2
Chlorine = Cl2
Sulfur = S8
bromine = Br2
Iodine = I2
Phosphorus = P4
Compounds
Ammonia = NH4
Nitric Oxide = NO
Notrogen dioxide = NO2
Sulfur dioxide = SO2
sulfur trioxide = SO3
Carbon Monoxide = CO
Carbon dioxide = CO2
Hydrogen chloride = HCl
Hydrogen sulfide = H2S
Water = H2O
Hydrogen Peroxide = H2O2
Carbon
molecules
methane = CH4
Methanol = CH3OH
Ethanol = CH3CH2OH
Ethanoic Acid / Acetic acid = CH3COOH
Ethane = C2H6
Ethene = C2H4
Ethyne = C2H2
Tetrachloromethane /
Carbon Tetrachloride = CCl4
Structures and Physical properties:
the
types of atoms
combining to form a substance
....
determines the type of bonding
forming the substance
...
types of bonding - determine the structure & physical properties of the substances
Matter /
substances can be classified according to the bonding involved:
There are
4 main types of substances:
discrete molecular substances
ionic substances
covalent substances
metallic substances
physical properties
of substances
when explaining physical properties consider...
the particles that make up the substance
the kind of forced between particles
Melting / boiling points
Solid - Liquid - Gas
For a substance to
melt:
particles of the solid
must be
separated
to allow the
particles to move
(and become a liquid)
For a substance to
boil:
particles of the liquid
must be further **separated
to
allow the particles to move
even more
(and become a gas)
to
separate
particles in a substance
=
forces between the particles must be overcome
Melting / boiling points are
determined by
the strength of the force that exsist
between the particles
of that substance:
High melting / boiling point:
Forces between the particles =
strong
...there is
lots of energy required
to
overcome the bonds and separate the particles
Low melting / boiling points:
forces between the particles =
weak
... so
not much energy
is required to overcome
the bonds and separate the particles
Conduction of electricity
in order for a substance to conduct electricity
it
must have 2 things
:
1-
a
charged particle
(an Ion, electron or a polar molecule)
2-
the particle must be able to
move freely
some substances will have
charged particles but not be able to conduct electricity until they're are melted/dissolved in water
...because they will have then become free moving
Solubility (in water)
forces holding together the particles
of the solute & of the solvents ...
must be broken
When a
substance dissolves in water.
..
particles of the substance separate
from each other then
spread evenly
though the water
when the** forces between solute particles
are similar strength to those between
the solvent** water molecules
... the
substance is easily dissolved in water
(as
forces between water molecules are relatively strong
)
Like dissolves like
polar molecules
generally dissolve in
polar solvents
Non-polar molecules
generally dissolve
best in
non-polar solvents
solute
=
substance being dissolved
solvent
= (water)
molecules doing the dissolving
when particles of the solvent mix attractions are made and broken depending on their polarity
when solvent molecules move apart,
...they break attractions that will later be remade between the solute and solvent (now seperated) particlces
Appearance
substances may appear
crystalline
or non-crystalline (amorphous)
:
-
Crystals form
when
particles or a solid arrange in a fixed geometric pattern
, that
repeats
over and over again in
3D
All the crystals formed of a particular substance will be similar shapes
molecular substances:
Examples:
I2, Cl2, CO2, S8, He,
NH3, CH4, CCl4, CHCl3
Molecular substances
= substances made up of
'separate' molecules
, held to each other with
weak inter molecular forces
they can be divided
into
2 groups:
Polar
molecules
electrons are not spread evenly
over the molecule
have permanent charge separation
over the whole molecule
Permanent dipole (attraction)
Attractive forces
between the opposite dipoles of the different molecules create/
hold together the molecular substance
through this attraction
Non- polar
molecules
electrons
in the the molecule are
continuously moving
, so they
are spread out
over the molecule
don't have positive and negative parts of the molecule
Don't have permanent charge separation
over the molecule
Extremely weak forces exist between molecules
, witch causes the attractive force between neighboring molecules
at a single instance a small dipole may exist
(due to unsymmetrical distribution of the moving electrons)
...there is a
temporary charge separation
,
... this causes the temporary attraction within the molecule
As the
mass of electrons increases:
the
mass of the molecule increases
the
electron cloud size increases
... so the force becomes stronger
properties
of
molecular substances:
Solubility in water
(or other polar solvents)
Forces between (
solute
) molecules are
weak
Forces between (
solvent
) water molecules
are relatively
strong
'most' molecular substances have
low solubility
in water
since **solute and solvent inter molecular forces
are different magnitudes** (so they aren't compatible)
(however
some molecules are
sufficiently polar to dissolve in water
)
solubility in non-polar
solvents
forces between molecules of non-polar solvents
= weak inter-molecular forces
most molecular substances have
inter-molecular forces of similar strengths,
to the other non-polar substance in the reaction
... therefore, **most molecular substance
will dissolve in non-polar solvents**
melting & boiling points
the substances are
made up of molecules and weak inter molecular forces
that exist between the molecules
the molecules are held together with
weak inter molecular forces
;
.... so only a
small amount of energy is
needed to separate the molecules
... so the substance can be
melted / vaporized easily
so molecular substances have
low melting / boiling points
molecules easily seperatd
= vaporize easily
= particles in gas state
= detect presence of substance in air
= smelt /
smell
conduction of electricity
molecular substances don't contain charged particles
... therefore
don't conduct electricity
4x different structures
;
extended networks
ionic substances
metallic substances
covalent netwerk substnaces
Ionic substances
substances made up of ions.
positive and negative ions are found in
a repeating pattern
in a
3D
arrangement
(a regular arrangement of particles = A lattice)
An Ionic bond = The
attraction between
2 oppositely charged ions
= electrostatic attraction
(the force between the ions is
quite strong
)
the
Empirical formula (E.F.)
of an ionic compound
...
tells you the ratio of ions
in the substance,
(not the 'actual' number of ions)
there are
no molecules
on ionic solids
... they are all
called; an Ionic substance
properties
of an
ionic substance:
Melting / Boiling point
substance
made up of positive & negative ions
...that are strongly attracted to each other
strong forces between the ions
...**
lots of energy required
to overcome
the forces and separate the ions
...
in order to melt / vaporize the substance
...
therefore, ionic solids have
high melting / boiling points**
Conduction (of electricity)
Ionic substances contain charged particles
(positive and negative ions).
To conduct electricity
, substances must both...
contain
charged particles
particles must be
free moving
In a
solid state = the ions are fixed in position
(unable to move)
... so the solid
won't conduct
When
melted the ions
become separated
and
able to move freely
... as molten / liquids they
will conduct
When ionic substances
dissolve in water
= the
ions separate
and are able to move freely
... so in solution ions
will conduct
solubility
In
Non-Polar
solvents:
Forces
between Non-polar solvent
=
too weak to attract the ions
in the solute
... so they are unable to pull the ions 'out' of the lattice
(
unable to separate the ions
)
Ionic substances
do not dissolve in Non-polar solvents
In
water / polar
solvents)
when ionic substances are 'added' to water
...
the
charged ions
in the substance are
attracted to
the high polarity (charged) water molecules
this attraction is sufficiently strong to 'pull'
the ions out of the ionic lattice
How
this happens:
1- the
negative 'end'
of the water molecule
= is attracted to the
positive ion
2 - the
positive 'end
' of the water molecule
= is attracted to the
negative ion
these 2 things
reduce the attraction
between the ions
(to each other)
...so they are
able to be separated
H2O can also surround the ion,
so the bond is weakened
Hardness:
Ionic substances are hard because of the strong ionic bonds,
However they are also
brittle
because;
...
attempts to distort / break / move
the ionic crystals
results in ions of 'like charges' coming together
/ in contact
... like charges repel
.. so the resulting repulsive forces push the lanes of ions apart
... the ionic crystals/ substances "cleave" apart
Metallic Substances
:
the
movement of electrons in random
,
they have
no particular direction
... so
metallic bonding = a non-directional force
Non directional force
= bonding has no direction / is random
Metallic
substances
= substances where
atoms are held together with metallic bonding
Metallic
bonding
= attraction between freely moving electrons at the nuclei of neighboring atoms
the valence electrons are loosely held so they
can be attracted to the nuclei of neighboring atoms,
this is metallic bonding and is what binds the structure
made up of Atoms
the atoms are packed closely together
lattice arrangement
metals have a
small number of valence electrons
... therefore, there is
space available in the outer shell
... so the
electrons can move
valence electrons are
not 'permanently' attached to
atoms
valence elections are able to move from one atom to the next within the substance but
no electrons are 'lost'
charge on a metal substance overall = zero
properties
of
metallic substances:
Conduction of heat:
metals =
good conductors of heat
... particles
collide with neighboring particles
and pass on kinetic energy**
.. this is heat conduction
not only the atoms vibrate, but the free moving electrons
.. and
electrosn tranfer (heat) energy much faster than atoms
Malleability / ductility
can be hammered & flattened (malleable)
can be pulled into wires (ductile)
Atoms are arranged in ordered layers
and
held together with non-directional bonding
... when a force is applied **layers of atoms
can slip over each other**
... because of non-directional bonding this **can occur
without breaking the structure**
Density:
Metals have a
high density
... due to
close packed arrangements
of atoms
(the 3D lattice)
Metallic lustre:
metals
= shiny
... because the valence electrons absorb / emit light energy
Conduction of electricity:
-
moving valence electrons
from one atom to another
...has
free moving charge
...has charged particles (the ions)
... therefore are
good conductors
Solubility:
All
metals are insoluble in all solvent
... metallic bonding =
too strong
... solvent particles can't attract metal atoms sufficiently
...
can't pull the atoms out of the Lattice
Melting / Boiling points
atoms held together by
metallic bonding = fairly strong
... you must
break 'strongish' bonds
to separate the atoms
... must separate in order to melt
...
lots of energy required to separate
and therefore melt
...
high melting / boiling points
Extended network
Substances where the
pattern of particles is
repeated over and over
many times
Covalent network
substances
Covalent network / giant covalent /
giant molecular /macro molecular
-substances
covalent substances = substances witch contain covalently bonded atoms arranged in an extended network
extended networks can be
arranged in 2 ways
:
2 dimensional covalent networks
(2D)
3 dimensional covalent networks
(3D)
2D covalent networks
(example)
Graphite
has a
layer structure
... each carbon (C) atom
bonds to 3 other carbon atoms
... each C atom has a remaining /
extra valence electron
witch is delocalised
... these
delocalised electrons are not associated
with a particular C atom
... instead the delocalised electrons
moves
throughout the layers
of C atoms
.. the delocalised electrons
create temporary dipoles
... so layers of C atoms are
held together by
weak inter-molecular bonds
Properties
of Graphite:
High melting point:
overall covalent networks have high melting / boiling points (because they must break the covalent bonds within the layers)
Covalent bonds between atoms = very strong
...
lots of energy needed to overcome these bonds
... even more energy required to separate the atoms
... High temp. need (lots of energy)
... have
high melting / boiling points
Inter molecular bonds between layers = weak
... therefore,
not much energy needed
to
overcome and separate these bonds
... lower temp. needed
...
low melting point
Soft, flaky, slippery / greasy solid
forces in between the layers of atoms
= weak inter molecular forces
... these forces between layers are easily broken
... therefore,
layers slip of each other easily
Graphene = 1 layer of graphite
.. this isn't soft because it is only one layer and
therefore
doesn't contain the weak inter molecular forces
Conducts electricity:
Delocalised electrons freely move
throughout the layers of C atoms
... they have free moving charge
...
Covalent networks are very good electrical conductors
Insoluble in all solvents
No attraction occurs between
solvent molecules and carbon atoms
.. there is no attraction to overcome the covalent bonds
(within the layers)
... so the atoms
can't be pulled out of the structure
3D covalent networks
(example)
Diomond
Each carbon atom is covalently bonded to 4 other C atoms
in a repeating tetrahedral arrangement
Properties
of Diamond:
Very high melting / boiling point
(higher than graphite)
Bonds between
all
C atoms =
covalent bonds = very strong
...
large quantity of energy
needed to break bonds
.. high temp. for lots of energy
...
melting point is very high
has
no weak inter molecular forces,
...as all the carbon atoms are covalently bonded
to another carbon atom
Very Hard
because the
strong covalent bonds exist in 3D
= the structure is strongly held together
diamond is one of the hardest known substances
(it is used to cut and engrave glass)
does
Not conduct electricity
there are
no spare valence electrons
because
each C atom is bonded to C other atoms
...the
valence electrons are held together tightly
in covalent bonds between the C atoms
... electrons are not free moving
... there is
no free moving charge
... unable to conduct electricity
Insoluble in all solvents:
-
no reaction occurs between solvent molecules
and carbon molecules
.. can't overcome the covalent bonds
...
atoms can't be pulled out of the structure
Silica / Silicon dioxide (SiO2)
each silicon atom is covalently
bonded to 4 oxygen atoms
each oxygen atom is covalently
bonded to 2 silicon atoms
... (this pattern is repeated throughout the structure)
has a bent / v-shape arrangement
bond angle = 109 degrees
Properties
of silicon dioxide:
very high melting point:
Bonds between silicon and oxygen
are
covalent bonds
with are
very strong
... each covalent bond must be broken
.. requires lots of energy to separate
..
melting requires separating atoms
/ small groups of atoms
Very Hard
...
strong covalent bonds exist in 3D
... so the structure is held together strongly
Does
not conduct
electricity
all **valence electrons are held tightly
in covalent bonds** between atoms
... electrons are not free moving
...
no free moving charge
...can't conduct electricity
Insoluble in
all solvents
**no reaction occurs between the solvent molecules
and the carbon and oxygen molecules**
... can't overcome the covalent bonds
... atoms
can't be pulled out of the structure
Silicon:
has a grey colour and metallic lustre
structure is
similar to diamond
Silicon Carbide (SiC):
One of the hardest known substances
each
carbon atom is covalently bonded to 4 silicon atoms
each silicon atom is covalently bonded to 4 carbon atoms
molecular substances:
Energy
changes
chemical changes
are
accompanied by energy /
heat changes
, as the atoms of the reactants are rearranged to form the products
A chemical change can:
be a change in state
a chemical reaction in which a
new substance is formed
Endothermic or Exothermic reactions
are chemical changes ... so they
have energy changes
Exo
thermic reactions
Release heat energy into the surroundings
Gas
to
liquid
to
solid
The
reactants have more energy stored in them
than will be needed for the products
... so the
extra energy is released as heat,
during the chemical change reaction
... ^rH reaction =
negative
low
activation energy
(EA)
- Bonds are formed
... must
gain / strengthen the attractive forces between particles
... so the process attains
'extra' energy
...
releases energy
into surroundings
products being formed require less energy than breaking the bonds of the reactants
... so due to the equation;
Products - reactants,
^rH = negative
Endot
hermic reactions
Absorb heat energy from the surroundings
solid
to
liquid
to
gas
The
reactants lave less energy stored in them than what is needed to make the products
... so the
reaction must gain energy
... energy is absorbed from surroundings during the chemical change / reaction
... ^rH reaction =
positive
High
activation energy
(EA)
Bonds are broken
... must
overcome the attractive forces between particles
, in order to break them
... process requires energy
... so it
absorbs energy
from the surroundings
products being formed require more energy than breaking the bonds of the reactants
... so due to the equation;
products - reactants,
the ^rH = positive
Enthalpy
(H)
Enthalpy = the heat content / energy stored in a substance
Enthalpy can't be measure,
only the chance in Enthalpy can be
^ rH = the change in Enthalpy that occurs during a reaction
^rH = H(products) - H(reactants)
you can't have negative energy,but you
can have negative change in energy / enthalpy
unit =
KJmol-1
During a chemical reaction;
bonds are broken and new bonds formed
(as the reactants are changed into their products)
overall ^rH = {bonds broken - {bond formed
{ = sum of the energy
Factors effecting the quantity
of energy exchanged
in an
Endo / Exo - thermic reaction:
The
'Nature' of the substance
Depending
on the
different substances reacting
... gives
different amount of energy changes
when the reaction occurs:
chemical bonds are broken at formed
^rH for the reaction = the sum of energy involved in bond breaking and making
when
bonds are broken
...
energy is required
so therefore,
absorbed
...
endo
thermic process / reaction
when
bonds are formed
... energy is in excess, therefore is released
...
exo
thermic process / reaction
Physical state
of the
reactants & products
Energy changes occur when a substance changes state
substances (of the same quantity) contain
more energy as a liquid than a solid
and more again as a gas.
Amount of substance
reacting:
The amount of a substance reacting will
determine how much heat is given / taken off
the greater amount of a substance involved in the reaction, the greater the energy change involved
large amount of substance = large amount of energy change
Energy change is given
per mole of a substance
involved n the reaction
Energy and changes
of state
change of state = a physical change
...when a physical change occurs
= there are energy changes
when...
particles
release / lose
energy
... kinetic energy
decreases
... particles move
more slowly
(this is an
exothermic process)
particles
absorb
energy
... kinetic energy
increases
... particles
move more rapidly
(this is an
endothermic process
)
Solid - liquid - gas
attractive forces between particles
of the substance must be
overcome
so they can
move more
/ faster
... so
bonds are broken
... energy is required / absorbed
...
Endo
thermic
Gas - Liquid - solid
particles come closer together (
move less
) so new
attractive forces are formed
... bonds are formed
... energy is released
Exo
thermic