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Chapter 6: Problem 73

The convention of arbitrarily assigning a zero enthalpy value for the most stable form of each element in the standard state at \(25^{\circ} \mathrm{C}\) is a convenient way of dealing with enthalpies of reactions. Explain why this convention cannot be applied to nuclear reactions.

Short Answer

Expert verified
The convention of assigning a zero enthalpy value to the most stable form of an element cannot apply to nuclear reactions, as nuclear reactions involve not just the energy of the electrons in the atomic orbitals, but also the energy contained in the nucleus. Thus, the energy scales in nuclear reactions are vastly different from those in chemical reactions.

Step by step solution

01

Understanding enthalpy and thermochemistry

Enthalpy is a measure of heat content. In thermochemistry, it is convenient to assign a zero enthalpy value to the most stable form of each element in its standard state at \(25^{\circ} C\). This is because we are mostly interested in the changes in enthalpy (\(\Delta H\)) when chemical reactions occur, not absolute values.
02

Understanding nuclear reactions

Nuclear reactions, on the other hand, involve changes in the nucleus of an atom, often with a significant change in the number and types of particles. The energies involved are much larger than in chemical reactions. Changes in the nucleus of an atom can lead to changes in the element itself.
03

Explaining the difficulty of the convention in nuclear reactions

Therefore, it is not possible to assign a zero enthalpy to the most stable form of each element in a nuclear reaction. The energy involved in nuclear reactions is not just the energy of the electrons in the atomic orbitals (as it is in chemical reactions), but also involves the energy contained in the nucleus of the atoms. Thus, the reference state for zero enthalpy in thermochemistry does not apply to nuclear reactions because it does not account for the energies involved in nuclear transformations.

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Most popular questions from this chapter

What is heat? How does heat differ from thermal energy? Under what condition is heat transferred from one system to another?

Define these terms: enthalpy, enthalpy of reaction. Under what condition is the heat of a reaction equal to the enthalpy change of the same reaction?

Which of the following standard enthalpy of formation values is not zero at \(25^{\circ} \mathrm{C} ? \mathrm{Na}(s), \operatorname{Ne}(g)\) \(\mathrm{CH}_{4}(g), \mathrm{S}_{8}(s), \mathrm{Hg}(l), \mathrm{H}(g)\)

Which of the following does not have \(\Delta H_{\mathrm{f}}^{\circ}=0\) at \(25^{\circ} \mathrm{C} ?\) \(\begin{array}{lllll}\text { He }(g) & \text { Fe }(s) & \text { Cl }(g) & \text { S }_{8}(s) & \text { O }_{2}(g) & \text { Br }_{2}(l)\end{array}\)

Which is the more negative quantity at \(25^{\circ} \mathrm{C}: \Delta H_{\mathrm{f}}^{\circ}\) for \(\mathrm{H}_{2} \mathrm{O}(l)\) or \(\Delta H_{\mathrm{f}}^{\circ}\) for \(\mathrm{H}_{2} \mathrm{O}(g) ?\)
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