Thermochemistry - calorimetric determination of the dissociation energy of hydrogen peroxide.

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THERMOCHEMISTRY: CALORIMETRIC DETERMINATION OF

THE DISSOCIATION ENERGY OF HYDROGEN PEROXIDE

PRELAB ASSIGNMENT

PROBLEMS:

1. What is the heat of formation DHf of O2(g) at 1 atm?

2. Using Hess' Law and the heats of reaction given in Table 1, determine the DH for the following reaction:

O2(g) + H2(g) ? H2O(g)

3. Using Hess' Law and the heats of reaction given in Table 1, determine the HO-OH bond energy.

I. PURPOSE AND SUMMARY

In this experiment, you will determine the molar heat of dissociation DHdis of the HO-OH bond in hydrogen peroxide.

H2O2(g) ? 2OH(g) DHdis = D (HO-OH) (1)

For this reaction the heat of dissociation is equal to the HO-OH bond energy. Since it is difficult to measure the heat of this reaction directly, you will use Hess' Law to determine DHdis. Hess' Law states that since the enthalpy is a function of state, it does not matter how the final state is obtained. In other words, the final state is independent of the path taken. Hess' Law is exceedingly useful for it allows us to calculate enthalpy changes which are difficult to