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2.3.1 Enthalpy Changes
- exothermic reaction
- gives out heat
- Delta H = -ve
- temperature of surroundings ^^^
- e.g combustion
- gives out heat
- Calculating enthalpy change
directly
- expt.
- Q=MCAT
- Q=MCAT
- expt.
- Calculating enthalpy changes indirectly
- Combustion = arrows up
- Formation = arrows down
- Combustion = arrows up
- Definitions
- Activation energy =
minimum energy
req. to break bonds
& initiate reaction
- Standard
conditions =
100 degrees 1
atmosphere
- DeltaH of reaction =
the enthalpy change
when the products
as specified in an
equation react
together under
standard conditions
- DeltaH of formation =
The enthalpy change
that occurs when one
mole of a compound is
formed from it's
constituent elements in
their standard states
under standard
conditions
- DeltaH of
Combustion =
the enthalpy
change when
one mole of a
substance
reacts
completely with
1 mole of
oxygen under
standard
conditions
- Average Bond Enthalpy = average
enthalpy change that takes place
when breaking by homiletic fission,
1 mole of a given type of bond in
the molecules of a gaseous species
- Hess's Law = states that if there
is more than one route for a
reaction and the initial and final
conditions are the same then the
total enthalpy change for each
route is the same
- Activation energy =
minimum energy
req. to break bonds
& initiate reaction
- Endothermic Reaction
- Takes in heat
- Delta H = +ve
- Temp of surroundings = down
- e.g Thermal decomposition
- Takes in heat
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