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N-7
The calorimeters being used are reasonably good insulators. During some reactions, the observed
temperature drop might be extremely slow, so the slope may be very close to zero. In these cases, the
maximum temperature reached (t
max
) may be very close to t
e
(t
max
will approximately equal t
e
.)
In Part I of this experiment you will measure the heat of the reaction of magnesium powder with 1.0 M
HCl and the heat of reaction of magnesium oxide with 1.0 M HCl. Both reactions are exothermic. You
will assume that all of the heat released by each reaction is absorbed by the solution. All solutions are
dilute, which means that they can be treated as water for the purpose of calorimetric calculations, with a
specific heat capacity of 4.184 J/g
C and a density (1.00 g/mL) (see example calculation below). The
calculated heats of reaction will be combined with ?H
f
of MgO
(s)
to calculate ?H
f
of. H2O
(l)
In Part II, ?H
rxn
, for the reaction represented by equation (10), will be determined as in Part I except
that the heat of solution for anhydrous Na2SO
4(s)
is given (- 4.43 kJ/mol).
In Part III, you will measure the heat released by neutralization of HCl with NaOH and
CH3COOH(acetic acid) with NaOH. Unlike Parts I and II, both reactants are in aqueous solutions. As
a result, the mass of the water to be used in the calculation of the heat transferred will be the sum of the
mass of the acidic solution, and of the mass of the hydroxide solution. Once again, you will assume that
the HCl, CH3COOH and NaOH solutions have the same properties as pure water. Also, because all
reagents are in aqueous solution and the reaction is very fast, you do not need to monitor the change in
temperature with time as you did in part I and II . Once the reagents are added, allow enough time for
the thermometer to respond to the change in temperature of the solution (~45 seconds) before
recording the final temperature.
EXAMPLE CALCULATION
In calorimetric experiments, it is important to remember that you are not directly measuring the heat
given off by the reaction. Instead you are measuring the change in temperature of the solution due to the
heat released or absorbed by the reaction. In this experiment (as in your textbook), you assume that
all of the heat that is released or absorbed by the reaction is absorbed or released by the
