a2 ocr chemistry enthalpy definitions

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Emily Summers
Standard Enthalpy Change of Formation
One mole
of
compound
is
for
med
fr
om
i
t'
s const
it
uent
el
ement
s i
n t
hei
r
standar
d st
ates
under
st
andar
d
condi
ti
ons
Nor
mal
ly
exothermic
in
ioni
c
compounds
K(s)
+
½ Cl
2
(g)
KCl
(
s)
437 KJ Mol1
Standard Enthalpy Change of Atomisation
One
mol
e of
gaseous
atoms
i
s f
ormed
fr
om
it
's
element
i
n i
t
's
standar
d st
ate
under
st
andar
d condi
ti
ons
Al
ways
endothermic
as
bonds
are
broken
K(s)
K(g)
+89 KJmol1
First Ionisation Energy
One
mol
e of
gaseous
1+
ions
is
for
med
fr
om
one
mol
e of
gaseous
atoms
Endothermic
because
the
elect
ron
lost
must
over
come
the
att
ract
ion
fr
om
the
nucl
eus
to
be
removed
+
K(g)
K (
g)
+ e +419 KJmol1
Second Ionisation Energy
+ +
One
mol
e of
gaseous
2 i
ons
are
for
med
fr
om
one
mol
e of
gaseous
1
i
o ns
Endothermic
because
the
elect
ron
lost
must
over
come
the
att
ract
ion
fr
om
the
nucl
eus
to
be
removed
+ 2+
Ca (g)
Ca (
g)
+ e +1145 KJmol1
First Electron Affinity
One
mol
e of
gaseous
1
ions
are
for
med
fr
om
gaseous
atoms
Exothermic
as
the
elect
ron
is
att
ract
ed
to
the
out
er
shel
l
of
an
atom
by
the
nucl
eus
Cl
(g)
+
e
Cl (
g)346KJ mol1
Second Electron Affinity
One
mol
e of
gaseous
2
ions
for
med
fr
om
gaseous
1
ions
Endothermic
as
the
elect
ron
is
repel
led
by
the
1
i
o n
that
must
be
over
come

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Emily Summers
2
O (
g)
+ e
O (
g)
+798 KJ mol1…read more

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