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RP2: Enthalpy change measurement
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Amirah A
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Cards (10)
Assumption made in calorimetry:
Energy
transferred to the
water
from reacting chemicals is
equal
to the
energy
released by the reaction
Sources of error:
Heat
loss
Incomplete
combustion of fuel
Heat
energy transferred to the metal
calorimeter
Some fuel
evaporates
Improvements to minimise sources of error:
Add a
lid
Insulate
sides of calorimeter
Reduce
distance
between flame
Put sleeve around
flame
to
protect
it from draughts
Steps to measure an enthalpy change using cooling curve:
Record the
temperature
for a suitable time (
3
mins) before adding reactants together
Establish an
accurate
initial temperature
Mix
reactants then record temperature every
minute
until trend is seen
Plot a
graph
of temperature against time
Extrapolate
the cooling curve back to the point of addition
Establish a
theoretical
temperature change accounting for
heat
loss
Measuring an enthalpy of solution:
Measure
water
with
apparatus
Use
suitable
mass
Insulated
container and add known mass
Use
before
and
after
weighing method
Record
initial
temperature
Record
temperature
at
regular
timed intervals
Plot
temperature
v
time
Extrapolate
lines to point of
addition
and use Q=mcT
Types of calorimetry experiments:
Burning
a fuel
Adding
a solid to a solution
Adding
two solutions together
Reducing uncertainty using the same thermometer:
Use
larger mass
of
fuel
Reducing the percentage uncertainty when using solutions:
Increase
the
concentration
of the solutions
Describe how to find the enthalpy of solution:
Measure
water
with
measuring
cylinder
Mass of
100cm3
Into a
polystyrene cup
with a
lid
Add known
mass
of solid
Use before and after
weighing
method
Record initial temperature
three
times
Record temperature at
regular
timed intervals for
5
or more mins
Plot temperature
against
time
Extrapolate
back to the point of
addition
to find the
final
temperature and find temperature
change
Reducing the percentage uncertainty of calorimetry:
Larger
mass of solid used
Change the
concentration
of reagent or solution
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