Question at position 16 Which statement is false? Which statement is false? Cold water has a lower pH than hot waterKw = [OH—][H+]Water dissociation is endothermicAs T increases, Kw increases Clear my selection

Question

BlackTom AI · Accepted Answer

To tackle this question, we evaluate each statement about water autoionization and how temperature affects it.
Option 1: 'Cold water has a lower pH than hot water' This is false. In pure water at higher temperatures, Kw increases, meaning both [H+] and [OH-] rise, which lowers the pH from 7 toward more acidic values. Conversely, at cooler temperatures Kw is smaller, so [H+] is smaller and pH is closer to neutral or slightly above 7. Therefore cold water does not have a lower pH than hot water; the opposite is true.
Option 2: 'Kw = [OH—][H+]' This is a true statement. The water dissociation equilibrium yields Kw as the product of the hydrogen ion concentration and the hydroxide ion concentration, and the two are equal in pure water, giving Kw = [H+][OH−]. The order of factors in a product does not matter, so this representation is correct.
Option 3: 'Water dissociation is endothermic' This is true. The process of autoionization of water absorbs heat (enthalpy change > 0). Since the equilibrium shifts toward greater ion formation with increasing temperature, the dissociation is endothermic.
Option 4: 'As T increases, Kw increases' This is true. Kw is temperature dependent and increases with rising temperature for water, reflecting the endothermic nature of the dissociation reaction. Higher temperature yields higher [H+] and [OH−], thus a larger Kw.

Question at position 16 Which statement is false? Which statement is false? Cold water has a lower pH than hot waterKw = [OH—][H+]Water dissociation is endothermicAs T increases, Kw increases Clear my selection单项选择题

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