The dissociation of water into H3O+ and OH– ions depends on temperature. At 0 °C the [H3O+] = 3.38 x 10–8 M, at 25 °C the [H3O+] = 1.00 x 10–7 M, and at 50 °C the [H3O+] = 2.34 x 10–7 M. c. Is the dissociation of water endothermic or exothermic?

Ch.10 Acids and Bases

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McMurry 8th Edition

Ch.10 Acids and Bases

문제 99c

10장, 문제 99c

The dissociation of water into H₃O⁺ and OH^– ions depends on temperature. At 0 °C the [H₃O⁺] = 3.38 x 10^–8 M, at 25 °C the [H₃O⁺] = 1.00 x 10^–7 M, and at 50 °C the [H₃O⁺] = 2.34 x 10^–7 M.
c. Is the dissociation of water endothermic or exothermic?

검증된 단계별 안내

Step 1: Understand the relationship between temperature and the dissociation of water. The dissociation of water into H₃O⁺ and OH⁻ ions is influenced by temperature, and the equilibrium constant (Kw) increases as temperature increases.

Step 2: Recall the principle of Le Chatelier's Principle. If a reaction is endothermic, increasing temperature will favor the forward reaction (more dissociation). If a reaction is exothermic, increasing temperature will favor the reverse reaction (less dissociation).

Step 3: Analyze the data provided. At higher temperatures (25 °C and 50 °C), the concentration of H₃O⁺ increases compared to lower temperatures (0 °C). This indicates that the dissociation of water is favored as temperature increases.

Step 4: Connect the observation to thermodynamics. Since the dissociation of water is favored at higher temperatures, this suggests that the process absorbs heat, which is characteristic of an endothermic reaction.

Step 5: Conclude that the dissociation of water is endothermic based on the increase in [H₃O⁺] with temperature, consistent with the absorption of heat during the dissociation process.

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Dissociation of Water

The dissociation of water refers to the process where water (H₂O) breaks down into hydronium (H₃O⁺) and hydroxide (OH⁻) ions. This equilibrium is influenced by temperature, as changes in temperature can shift the concentrations of these ions in solution. Understanding this process is crucial for analyzing how temperature affects the acidity and basicity of water.

Endothermic vs. Exothermic Reactions

Endothermic reactions absorb heat from their surroundings, leading to a decrease in temperature, while exothermic reactions release heat, resulting in an increase in temperature. The classification of a reaction as endothermic or exothermic can be determined by observing temperature changes during the reaction. This concept is essential for understanding the thermal dynamics of the dissociation of water.

Temperature Dependence of Equilibrium

The temperature dependence of equilibrium states that the position of equilibrium in a chemical reaction can shift with changes in temperature, as described by Le Chatelier's principle. For the dissociation of water, an increase in temperature typically favors the formation of products (H₃O⁺ and OH⁻), indicating that the reaction is endothermic. This principle helps in predicting how temperature variations affect the dissociation process.