Chemistry · Acids, Bases and Salts

The ionic product of water (Kw) is the product of the concentrations of hydrogen ions (H+) and hydroxide ions (OH-) in water. It is defined by the equation:

Kw = [H+][OH-]

At 180°C, the value of Kw is given as 0.64×10-14, and at 25°C, it is given as 1×10-14.

We know that the value of Kw is temperature dependent. As the temperature increases, the value of Kw also increases. The increase in Kw with increasing temperature is an endothermic process. Endothermic processes absorb heat or energy from the surroundings, increasing the value of Kw.

The ionic product of water, K_w, is the equilibrium constant for the auto-ionization of water:

H_2O(l) \rightleftharpoons H^+(aq) + OH^-(aq)

The value of K_w is given as 0.64 \times 10^{-14} at 180 °C and 1 \times 10^{-14} at 25 °C.

We observe that the value of K_w increases as the temperature increases (0.64 \times 10^{-14} < 1 \times 10^{-14}). According to Le Chatelier's principle, if increasing the temperature shifts the equilibrium to the right (favoring the formation of H^+ and OH^- ions), then the forward reaction (the auto-ionization of water) must be endothermic. An endothermic reaction absorbs heat, so increasing the temperature will favor the products.

* Exothermic process: If the process were exothermic, increasing the temperature would shift the equilibrium to the left, decreasing the concentration of H^+ and OH^- ions, and thus decreasing the value of K_w. This contradicts the given data.

Vaporization process: Vaporization is the phase transition from liquid to gas. While temperature affects vaporization, the given values of K_w relate to the concentrations of ions in the aqueous phase, not the gaseous phase.

Change of H₂O into O₂ and H₂: This option describes the decomposition of water into hydrogen and oxygen gas (2H_2O(l) \rightarrow 2H_2(g) + O_2(g)), which is a different chemical reaction than the auto-ionization of water and is not directly related to the ionic product K_w.