Detailed revision notes for AQA A Level Chemistry - 3.1.4. energetics.
includes:
- hess‘s law cycle
- mean bond enthalpy
- standard enthalpy of formation
- all formulae needed
These study notes allowed me to get an A* at end of year 12 exams.
3.1.41 .
ENTHALPY CHANGE
exothermic reaction surroundings include : -
solvent ; air around the test tube ; test tube ,
I heat to the
anything dripping
↳ releases
energy surroundings into the test tube
energy R -
has negative enthalpy changy example : combustion of fuels
f.
µ,
P
oxidation of
carbohydrates in bodies of plants animals
reaction of H2O and calcium oxide ( quicklime)
rxn
endothermic
↳
absorbs heat from the surroundings examples decomposition of limestone by heating:
energy has positive enthalpy change photosynthesis ( energy supplied by sunlight)
a P -
AH
dissolving certain salts water
+
ammonium in
R
rxn
definitions :
the heat required to temperature of
Ig of substance
specific heat
capacity increase
by 1°C
:
of
enthalpy :
measure of the total
energy a
system
heat
energy
: the portion of the potential & kinetic
energy
of a substance that's responsible for the temperature of substance
first law of thermodynamics :
during Chem reaction
energy
cannot be created nor destroyed can be converted
-
.
,
chemical made up of components kinetic of the motion of particles in substance
energy is a
:
energy measure
:
-
potential energy measure -
of how
strongly these particles interact with 1 another
enthalpy change CAH) :
the heat
energy change
under conditionsof constant pressure
standard measured under standard conditions 100hPa & stated temperature 129814
enthalpy change the heat
change
: :
enthalpy of combustion ISHII the enthalpy change
:
when I mole of substance is burned completely in oxygen
under standard conditions ,
with
everything in standard state
enthalpy of formation IsHitt the :
enthalpy change when I mole of substance is formed from its elements
under standard conditions , with
everything in standard state
Hess 's law change of of
:
the enthalpy cheatI a reaction is independent the reaction route taken
Mean bond enthalpy : the
enthalpy change when I mole of gaseous) covalent bonds
( are broken
averaged range of compounds
>
over a
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