Gas A2 reacts with gas B2 to form gas AB at a constant temperature. The bond energy of AB is muc

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Gas A2 reacts with gas B2 to form gas AB at a constant...

Gas $\mathrm{A}_{2}$ reacts with gas $\mathrm{B}_{2}$ to form gas $\mathrm{AB}$ at a constant temperature. The bond energy of $\mathrm{AB}$ is much greater than that of either reactant. What can be said about the sign of $\Delta H ? \Delta S_{\text {sumr }} ? \Delta S ?$ Explain how potential energy changes for this process. Explain how random kinetic energy changes during the process.

Key Concepts

Exothermic Reaction

This concept refers to processes that release energy due to forming bonds that are stronger (i.e., lower in energy) than those in the reactants. When the new bond has a greater bond energy than the bonds being broken, the reaction releases energy, leading to a negative ?H. This shift in energy is critical in predicting the heat evolution of a reaction.

Entropy Change in Gas-phase Reactions

Entropy (?S) measures the randomness or disorder of a system. When a reaction reduces the number of gas molecules, as in the case of two reactant molecules forming one product molecule, the system’s disorder decreases, resulting in a negative ?S. This concept is important in understanding how changes in molecular count and arrangement can impact the overall spontaneity of a reaction.

Potential Energy Change

In chemical reactions, potential energy is primarily associated with the bonds between atoms. The formation of a stronger (lower-energy) bond results in a decrease in the system's potential energy. This concept explains how energy is stored and released in bonds, and it is central to understanding reaction energetics.

Random Kinetic Energy

Random kinetic energy refers to the energy associated with the motion of particles. When a reaction is exothermic, the energy released from the drop in potential energy raises the random kinetic energy of the particles, typically observed as an increase in temperature. This concept bridges the gap between molecular-level energy changes and observable macroscopic properties like temperature.

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