Use Le Chatelier's principle to predict the effect that the change given in the first column of the following table has on the quantity in the second column for the following equilibrium system: $$ \begin{gathered} 5 \mathrm{CO}(\mathrm{g})+\mathrm{I}_{2} \mathrm{O}_{5}(\mathrm{~s}) \rightleftharpoons \mathrm{I}_{2}(\mathrm{~g})+5 \mathrm{CO}_{2}(\mathrm{~g}) \\\ \Delta H^{\circ}=-1175 \mathrm{~kJ} \end{gathered} $$

Chemical equilibrium is a state in which the rates of the forward and reverse reactions are equal, resulting in no net change in the concentrations of reactants and products over time. It is vital to recognize that equilibrium does not mean that the reactants and products are present in equal amounts, but rather that their ratios are constant.

Consider a simple reversible reaction where the reactants A and B form products C and D:

• Forward reaction: A + B → C + D
• Reverse reaction: C + D → A + B

At equilibrium, the rate at which A and B react to form C and D is the same as the rate at which C and D revert back to A and B. This balance of rates ensures that the overall concentration of each species remains constant, though they may continue to react on a molecular level.

Exothermic reactions are characterized by the release of energy, usually in the form of heat, to the surroundings. The reaction enthalpy, denoted as \( \Delta H^\circ \), is negative for exothermic processes, indicating that energy is exiting the system.

For example, when you feel warmth from a chemical hand warmer, it is the result of an exothermic reaction occurring inside. This release of thermal energy is spontaneous and converts the reactants into products while emitting heat:

• Reactants → Products + Heat

The generated heat can influence the surrounding environment and, in a closed system, can also affect the reaction itself if temperature changes occur.

According to Le Chatelier's Principle, if the temperature of an equilibrium system is altered, the system will adjust to minimize the impact of this change. In the context of exothermic reactions, an increase in temperature injects additional heat, which the system counteracts by shifting the equilibrium to favor the reactants, effectively absorbing the excess heat.

Decreasing the temperature, on the other hand, removes heat from the system. As a result, the equilibrium will adjust by shifting toward the products, as the exothermic reaction releases heat, compensating for the lost thermal energy. This shift is predictable: if you cool down an exothermic reaction, expect more products to form as the system tries to maintain its balanced state.

Reaction enthalpy (\( \Delta H^\circ \)) plays a crucial role in determining how a chemical equilibrium responds to changes in temperature. A negative \( \Delta H^\circ \) signifies an exothermic reaction. When such a reaction is subjected to a temperature increase, Le Chatelier's Principle indicates that the system will shift to absorb the added heat, thus moving the equilibrium toward the reactants. Conversely, decreasing the temperature causes the equilibrium to shift toward the products to release heat and raise the system's temperature.

It is important to remember that while \( \Delta H^\circ \) provides information about the heat change during the reaction, it also predicts the direction of the equilibrium shift in response to temperature fluctuations. Recognizing the sign of \( \Delta H^\circ \) is thus essential for anticipating how equilibrium will re-establish itself under changing conditions.