In a reversible reaction, how are energy changes characterized?

In a reversible reaction, one direction is characterized as exothermic, while the opposite direction is endothermic. This means that during the forward reaction, energy is released to the surroundings, resulting in a temperature increase, while in the reverse reaction, energy is absorbed from the surroundings, leading to a decrease in temperature.

This interchange of energy between the two directions allows the reaction to be reversible; the products formed in one direction can be converted back into the reactants by absorbing the energy that was initially released. This principle is often illustrated by the example of the decomposition of ammonium chloride: when it is heated, it dissociates into ammonia and hydrogen chloride, an endothermic process that absorbs heat; conversely, when ammonia and hydrogen chloride react to form ammonium chloride, this is exothermic as it releases heat.

Understanding the energy changes associated with reversible reactions is fundamental in chemical thermodynamics, as it highlights how energy conservation plays a role in the dynamic nature of chemical reactions.