An explosion used five tons \((1\) ton \(=2000 \mathrm{lb}\) ) of ammonium nitrate \((\Delta E=-37.0 \mathrm{~kJ} / \mathrm{mol})\). (a) How much energy was released by the explosion? (b) How many grams of TNT \((\Delta E=-2.76 \mathrm{~kJ} / \mathrm{g})\) are needed to release the energy calculated in (a)? (c) How many grams of U-235 are needed to obtain the same amount of energy calculated in (a)? (See the equation in Problem 45.)

Understanding the enthalpy of reaction is crucial when studying energy changes in chemical reactions. Enthalpy, represented by the symbol \( H \), is a measure of the total heat content of a system at constant pressure. The enthalpy of reaction, or \( \Delta H \), refers to the heat change that occurs during a chemical reaction.

For exothermic reactions, such as the explosion of ammonium nitrate, the enthalpy of reaction is negative, indicating that energy is being released to the surroundings. In contrast, endothermic reactions absorb energy, resulting in a positive \( \Delta H \). The value for the enthalpy change in the given problem is \( -37.0 \mathrm{~kJ/mol} \), describing the amount of energy each mole of ammonium nitrate releases upon decomposition.

To calculate the total energy released in the explosion, one would multiply the enthalpy change per mole by the total number of moles of reactants consumed. Here, improved comprehension can be achieved by reassuring a firm grasp of the concept of moles and molar enthalpy change as indicators of energy per unit of a substance.

Chemical thermodynamics is the branch of chemistry that deals with the relationship between heat changes and chemical reactions. It encompasses the study of the energy and entropy of a system related to the spontaneity of a reaction.

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed. This is directly applicable when calculating the energy released by the explosion of ammonium nitrate and equivalent energy from TNT or U-235, as shown in the exercise. The amounts of ammonium nitrate, TNT, and U-235 calculated reflect the energy that they can release, which is conserved and follows the law of conservation of energy.

As students work through chemical thermodynamics problems, they should be mindful that variables such as temperature, pressure, and the nature of reactants and products significantly impact the thermodynamic quantities of a system. The challenge often lies in translating these abstract concepts into actual quantitative values, as in the given exercise.

Stoichiometry is the area of chemistry that pertains to the quantitative relationships between the reactants and products in a chemical reaction. It is based on the conservation of mass and the concept of the mole.

When utilizing stoichiometry to solve problems like the one given, one must first convert quantities into moles, as it allows for the comparison between different substances based on their molar ratios dictated by the balanced chemical equation. In this case, we began by converting the mass of ammonium nitrate into moles.

After determining the number of moles, the next step usually involves using the mole ratio to find the amount of another substance involved in the reaction, in terms of moles, grams, or energy released or absorbed. Students can improve problem-solving by clearly understanding and applying stoichiometric coefficients and the molar mass of each substance, essentially the heart of stoichiometry, to ensure accurate calculations and a strong conceptual foundation.