This isn't a difficult question. I'm sure LLM knows these things better than I do. Water is H-O-H; H+ and OH- both come from water. If there are no impurities,

This isn't a difficult question. I'm sure LLM knows these things better than I do. Water is H-O-H; H+ and OH- both come from water. If there are no impurities, then for every extra H+ there is an extra OH-, so it's not that they are "happen to be equal". They're born equal. Changing the temperature does change the concentrations of these ions so pH does change by definition. But the water remains neutral, since the ratio of H⁺ to OH⁻ is still 1:1