For would eventually pull away to form phen-H+,

For the first reaction (between ferroin
and HNO3), the results of the experiment indicate that the rate law

Rate = 0.0276F  (39.4oC)

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Rate = 0.124F    (53.6oC)

an activation energy of 89.7 kJ. The reaction was first order, meaning that the
rate of the reaction was dependent on the concentration of ferroin, but zero
order for the concentration of nitric acid, suggesting that the rate changed
independently of the concentration of nitric acid. The pre-exponential factor (A), suggests that there were 2.08 x 1014
collisions per minute at each temperature. These results are reasonable for the
most part. However, a few details of the experiments were unusual. For example,
the exact value of b at 39.4oC was negative, implying that the kobs2
was greater than kobs1. This should not have occurred because the
second experiment was more concentrated in nitric acid so the reaction should
have proceeded faster. An explanation for this is that some of the H+
ions were attracted by the water molecules, forming H3O+.
Since this is an equilibrium reaction, the H+ would eventually pull
away to form phen-H+, however this would result in a slower
reaction. On another note, while the activation energy seems to be reasonable
(activation energies are usually very high), it is possible that it is not
fully accurate due to the fact that the temperature would fluctuate around 40oC.
However, since the differences in temperatures was minimal, the percent error
of the calculated activation energy should not be too high, assuming that the
rest of the lab was carried out smoothly.

            The reaction mechanism must be
consistent with the rate law mentioned above, and must also add up to the
overall stoichiometry of the reaction as presented in the introduction. A
possible mechanism is

Fe2+ + 3phen  (slow)

+ 3H+ à 3phen-H+ (fast)

adds up to the overall reaction, taking note of the fact that the water is not
included in the mechanism because it is aqueous when it is with iron.

            In reaction (2), the rate law at
each temperature was

Rate = 0.0388F  (40oC)

Rate = 0.213F    (55oC)

an activation energy of 97.0 kJ for the rate determining step, suggesting that
97.0 kJ of energy is needed to in order for the reaction to proceed. The
pre-exponential factor was 5.92 x 1014 min-1, which means
that there were 5.92 x 1014 collisions per minute as the reaction
progressed at both temperatures. The rate law implies that the rate is only
dependent on the concentration of ferroin and not on the concentration of
copper ions. A possible mechanism for this reaction is

Fe(phen)32+ à Fe2+ +
3phen    (slow)

+ 3Cu2+ à 3Cu(phen)2+         (fast)

slow step is consistent with that rate law, and the stoichiometry of the
mechanisms match that of the overall reaction. Note that the second step does
not involve the collision of 6 molecules at the same time – this is nearly
impossible. Instead, it is implying that the step occurs three times.