Problem 49 - General Chemistry

Question

Nitric acid, a source of many nitrogen compounds, is produced from nitrogen dioxide. An old process for making nitrogen dioxide employed nitrogen and oxygen. $$ \mathrm{N}_{2}(g)+2 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) $$ The reaction absorbs \(66.2 \mathrm{~kJ}\) of heat per \(2 \mathrm{~mol} \mathrm{NO}_{2}\) produced. Is the reaction endothermic or exothermic? What is the value of \(q\) ?

Step-by-Step Solution

Answer

Endothermic reaction, q = +66.2 kJ.

Step 1: Understanding the Reaction Type

Check the heat flow in the reaction. If the reaction absorbs heat, it is considered endothermic. The given problem states that the reaction absorbs \(66.2 \mathrm{~kJ}\) of heat, indicating that it is endothermic.

Step 2: Evaluating Heat of Reaction, q

The problem specifies that the reaction absorbs \(66.2 \mathrm{~kJ}\) of heat for every \(2 \mathrm{~mol}\) of \(\mathrm{NO}_{2}\) produced. Hence, the heat of the reaction, \(q\), is \(+66.2 \mathrm{~kJ}\). The positive sign indicates that heat is absorbed from the surroundings, making it a positive value for an endothermic reaction.

Step 3: Concluding Reaction Type and q

The reaction is endothermic, confirmed by the heat being absorbed, and the calculated \(q\) value is \(+66.2 \mathrm{~kJ}\).

Key Concepts

Heat of Reaction

The heat of reaction is a vital concept in chemistry as it tells us whether a reaction absorbs or releases heat. This energy change is often expressed as "q". In chemical reactions, when heat is absorbed, the process is termed endothermic. Alternatively, when heat is released, the reaction is exothermic.

In our specific exercise involving the formation of nitrogen dioxide ( NO_2rom nitrogen ( N_2"]) and oxygen ( O_2"]) gases, the reaction absorbs 66.2 kJ for every 2 moles of NO_2"]] produced. This heat absorption indicates that the reaction is endothermic.

The positive value of q (+66.2 kJ) further supports the endothermic nature of this process. It reflects the energy required to drive this reaction forward, pulling heat from its surroundings.

Nitrogen Dioxide Production

Nitrogen dioxide ( NO_2"]) production is an important chemical process, especially in industrial chemistry. It involves combining nitrogen ( N_2"]) with oxygen ( O_2"]) to form nitrogen dioxide. Knowing the heat absorbed or released during this reaction is essential for managing reaction conditions.

This production process is endothermic, as discovered in the given problem statement. The reaction needs an input of 66.2 kJ of energy to create 2 moles of NO_2"]).

Understanding the endothermic nature of this reaction helps in fine-tuning the conditions needed to efficiently manufacture NO_2"]), which in turn is a precursor to making nitric acid and other nitrogen compounds.

Thermochemistry

Thermochemistry focuses on the study of heat energy associated with chemical reactions and changes of state. In this perspective, it's paramount to measure how heat flows in and out of a reaction.

In endothermic reactions, heat is absorbed, which is a central idea in thermochemistry. This exercise exemplifies thermochemical principles by showing how the reaction between nitrogen ( N_2"]) and oxygen ( O_2"]) to form nitrogen dioxide ( NO_2"]) absorbs a specific amount of heat.

By using these thermochemical principles, chemists can predict how much energy is required or released, helping to control the conditions under which reactions are conducted efficiently. This practice ensures optimal energy usage and safety in chemical processes.

Chemical Thermodynamics

Chemical thermodynamics is the study of energy transformations in chemical reactions. It helps us understand how energy interchanges during processes.

This exercise illustrates chemical thermodynamics by demonstrating an endothermic reaction where energy is absorbed. The given exercise shows that 66.2 kJ of heat is taken in to produce 2 moles of nitrogen dioxide ( NO_2"]).

Understanding these energy changes is crucial in chemical thermodynamics. It assists scientists and engineers in predicting reaction feasibility, designing energy-efficient processes, and ensuring reaction safety. Calculating q, the heat of reaction, is a fundamental aspect of analyzing these energetic transformations in chemistry.