Question

The thermite reaction, \(\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+2 \mathrm{Al}(s) \longrightarrow 2 \mathrm{Fe}(s)+\) \(\mathrm{Al}_{2} \mathrm{O}_{3}(s), \Delta H^{\circ}=-851.5 \mathrm{kJ} / \mathrm{mol},\) 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 \(\mathrm{Al}_{2} \mathrm{O}_{3}\) 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?

Short answer

The heat released per mole of Al₂O₃ produced in the thermite reaction is -851.5 kJ/mol. We cannot make a quantitative comparison with the energy released during the formation of alpha particles due to insufficient information provided. However, we can qualitatively state that the energy released during the formation of alpha particles is likely much greater than the heat released per mole of Al₂O₃ produced in the thermite reaction.

Step-by-step solution

Calculate the heat released per mole of Al₂O₃ produced

First, let's analyze the balanced chemical equation for the thermite reaction: \[Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(s) + Al_2O_3(s)\] We are given that the enthalpy change of this reaction, ΔH°, is -851.5 kJ/mol. Since this is a per mole value, we need to find the heat released per mole of Al₂O₃ produced. The reaction shows that 1 mole of Fe₂O₃ reacts with 2 moles of Al to produce 1 mole of Al₂O₃. Therefore, the -851.5 kJ/mol heat is released during the production of 1 mole of Al₂O₃. So, the heat released per mole of Al₂O₃ produced is -851.5 kJ/mol.

Evaluate the energy released when protons and neutrons combine to form alpha particles

An alpha particle consists of 2 protons and 2 neutrons. According to the question, we need to find the energy released when 2 moles of protons and 2 moles of neutrons combine to form 1 mole of alpha particles. Unfortunately, there is not enough information provided in the question to directly calculate or compare the energy. We would normally need mass values or binding energy information for protons, neutrons, and alpha particles to find the energy released during the formation of alpha particles. However, it can be generally inferred that the energy released in nuclear reactions, such as the formation of an alpha particle from protons and neutrons, tends to be much greater than the energy released by chemical reactions, such as the thermite reaction. In summary, without having access to the actual energy values for the formation of alpha particles, we cannot make a quantitative comparison with the energy released by the thermite reaction. However, we can qualitatively state that the energy released during the formation of alpha particles is likely much greater than the heat released per mole of Al₂O₃ produced in the thermite reaction.

Key concepts

Understanding Enthalpy Change

Enthalpy change, often represented as \( \Delta H \), refers to the heat energy absorbed or released during a chemical reaction at constant pressure. It is measured in joules per mole (J/mol) or kilojoules per mole (kJ/mol). A negative value for \( \Delta H \) indicates that the reaction is exothermic, which means it releases heat. In contrast, a positive value indicates an endothermic reaction, where heat is absorbed from the surroundings.

When dealing with the thermite reaction, the heat released is substantial, amounting to -851.5 kJ for every mole of aluminum oxide (\( Al_2O_3 \) produced. It's important to recognize that this value is not just an arbitrary number but rather a precise measurement of the energy exchange taking place, and it's directly connected to the amount of reactants used in the reaction.

One of the primary challenges in chemistry is not only the ability to measure such values but also the understanding of their implications in various contexts, such as industrial applications, safety considerations, and environmental impact.

The Exothermic Nature of Thermite Reactions

Exothermic reactions are fascinating chemical processes that release energy in the form of heat or light. The thermite reaction is a prime example of an exothermic reaction, with its heat being sufficient to melt iron. This characteristic is utilized in various applications, from the welding of railway tracks to the creation of incendiary devices.

Understanding the practicality of exothermic reactions extends beyond mere heat production. These reactions can be harnessed for energy generation, heating systems, and even in educational demonstrations to illustrate chemical concepts. The challenge for students is to interpret the implications of an exothermic reaction in terms of energy flow and reactant-to-product conversion, which is especially evident in the potent reaction between \( Fe_2O_3 \) and aluminum to produce molten iron and \( Al_2O_3 \).

Providing real-world examples of exothermic reactions can help students to connect theoretical chemical principles with tangible outcomes, encouraging a deeper appreciation and understanding of the topic.

Stoichiometry of the Thermite Reaction

Stoichiometry is the field of chemistry that involves the calculation of reactants and products in chemical reactions. It is a branch of chemistry that deals with determining the proportions of elements that combine during chemical reactions and can be considered the 'recipe' of chemistry.

In the context of the thermite reaction, stoichiometry enables us to quantify the exact amounts of reactants needed to produce a desired amount of product, in this case, \( Al_2O_3 \). For students, mastering stoichiometry is crucial as it forms the basis for predicting the outcomes of reactions, including the amount of energy release measured through enthalpy changes.

Application in Thermite Reaction

The balanced equation for the thermite reaction is an excellent stoichiometric representation, showcasing the conversion of \( Fe_2O_3 \) and \( Al \) to \( Fe \) and \( Al_2O_3 \). It is this precise ratio that allows us to determine the exact heat release per mole of \( Al_2O_3 \) produced. Such concepts are not just academic exercises; they are fundamental to the practical applications of these reactions, from industrial manufacturing to controlled demolitions.

When students grasp the idea that stoichiometry reflects the conservation of mass and the quantitative aspects of chemical reactions, they can better predict the amounts of reactants they would need and the volume of products they can expect, including the crucial factor of energy change.