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For the reaction H₂O(l) ⇌ H⁺(aq) + OH⁻(aq), K_w = 10⁻¹⁴ at 25°C 55.9 kJ mol⁻¹ of heat is evolved when one mole of H⁺(aq) reacts with one mole of OH⁻(aq) - VCE - SSCE Chemistry - Question 13 - 2004 - Paper 1
Question 13
For the reaction H₂O(l) ⇌ H⁺(aq) + OH⁻(aq), K_w = 10⁻¹⁴ at 25°C 55.9 kJ mol⁻¹ of heat is evolved when one mole of H⁺(aq) reacts with one mole of OH⁻(aq). At 80°C, ... show full transcript
Worked Solution & Example Answer:For the reaction H₂O(l) ⇌ H⁺(aq) + OH⁻(aq), K_w = 10⁻¹⁴ at 25°C 55.9 kJ mol⁻¹ of heat is evolved when one mole of H⁺(aq) reacts with one mole of OH⁻(aq) - VCE - SSCE Chemistry - Question 13 - 2004 - Paper 1
Step 1
K_w and pH for pure water
Answer
At higher temperatures, the value of K_w increases due to the endothermic reaction of water dissociation. Thus, at 80°C, K_w will be greater than 10⁻¹⁴. Since pure water remains neutral, the concentration of H⁺ ions will equal that of OH⁻ ions, resulting in a pH of less than 7.
Therefore, the correct choice is B: greater than 10⁻¹⁴ | greater than 7.