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Ch.21 - Nuclear Chemistry
Chapter 21, Problem 46

The thermite reaction, Fe2O31s2 + 2 Al1s2 ¡2 Fe1s2 + Al2O31s2, H = -851.5 kJ>mol, is one of the most exothermic reactions known. Because the heat released is sufficient to melt the iron product, the reaction is used to weld metal under the ocean. How much heat is released per mole of Al2O3 produced? How does this amount of thermal energy compare with the energy released when 2 mol of protons and 2 mol of neutrons combine to form 1 mol of alpha particles?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Thermodynamics and Enthalpy

Thermodynamics is the study of energy transformations, and enthalpy (ΔH) is a key concept that measures the heat content of a system at constant pressure. In the thermite reaction, the negative ΔH value indicates that the reaction is exothermic, meaning it releases heat. Understanding how to interpret ΔH allows us to calculate the heat released per mole of products formed, such as Al2O3.
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Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. In the thermite reaction, the coefficients indicate the molar ratios of reactants and products. By applying stoichiometric principles, we can determine the amount of heat released per mole of Al2O3 produced by relating it to the total heat released in the reaction.
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Nuclear Reactions and Energy Release

Nuclear reactions, such as the fusion of protons and neutrons to form alpha particles, release energy due to the conversion of mass into energy, as described by Einstein's equation E=mc². This energy release is typically much greater than that of chemical reactions. Comparing the energy released in the thermite reaction with that from nuclear fusion highlights the significant differences in energy scales between chemical and nuclear processes.
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Related Practice
Textbook Question

Cobalt-60 is a strong gamma emitter that has a half-life of 5.26 yr. The cobalt-60 in a radiotherapy unit must be replaced when its radioactivity falls to 75% of the original sample. If an original sample was purchased in June 2016, when will it be necessary to replace the cobalt-60?

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Textbook Question

The cloth shroud from around a mummy is found to have a 14C activity of 9.7 disintegrations per minute per gram of carbon as compared with living organisms that undergo 16.3 disintegrations per minute per gram of carbon. From the half-life for 14C decay, 5715 yr, calculate the age of the shroud.

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Textbook Question

Potassium-40 decays to argon-40 with a half-life of 1.27 * 109 yr. What is the age of a rock in which the mass ratio of 40Ar to 40K is 4.2?

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Textbook Question

How much energy must be supplied to break a single aluminum-27 nucleus into separated protons and neutrons if an aluminum-27 atom has a mass of 26.9815386 amu? How much energy is required for 100.0 g of aluminum-27? (The mass of an electron is given on the inside back cover.)

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Textbook Question

The atomic masses of hydrogen-2 (deuterium), helium-4, and lithium-6 are 2.014102 amu, 4.002602 amu, and 6.0151228 amu, respectively. For each isotope, calculate

(c) the nuclear binding energy per nucleon.

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Textbook Question

The atomic masses of nitrogen-14, titanium-48, and xenon-129 are 13.999234 amu, 47.935878 amu, and 128.904779 amu, respectively. For each isotope, calculate (a) the nuclear mass.

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