中和反应Neutralization (chemistry)

HCl + NaOH → NaCl + H₂O；H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O。酸与碱性氧化物、碳酸盐和氨反应也生成盐，如 CuO + H₂SO₄ → CuSO₄ + H₂O，CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂，NH₃ + HCl → NH₄Cl。

HCl + NaOH → NaCl + H₂O; H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O. Acids also form salts with basic oxides, carbonates and ammonia: CuO + H₂SO₄ → CuSO₄ + H₂O, CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂, NH₃ + HCl → NH₄Cl.

在稀溶液中，酸与碱发生中和反应生成 1 mol 水时的焓变称为中和焓。强酸与强碱的中和焓几乎相同，约 −57 kJ mol⁻¹，因为反应实质都是 H⁺ + OH⁻ → H₂O。弱酸或弱碱参与时，中和焓的绝对值略小，因为弱电解质的电离需要吸收能量。

The enthalpy change when an acid and alkali react in dilute solution to form one mole of water is the enthalpy of neutralisation. For strong acids with strong bases it is almost the same, about −57 kJ mol⁻¹, because the reaction is always H⁺ + OH⁻ → H₂O. With a weak acid or base it is slightly less exothermic, because ionising the weak electrolyte absorbs energy.

中和反应用于酸碱滴定测定浓度；农业上用熟石灰改良酸性土壤；医学上用氢氧化镁、碳酸氢钠等抗酸药中和过多的胃酸；工业上用石灰中和酸性废水。中和后溶液的 pH 不一定为 7：强酸弱碱盐溶液呈酸性，强碱弱酸盐溶液呈碱性。

Neutralisation is used in acid–base titrations to find concentrations; slaked lime is added to acidic soils; antacids such as magnesium hydroxide and sodium hydrogencarbonate neutralise excess stomach acid; lime neutralises acidic industrial waste water. The resulting solution is not necessarily pH 7: salts of a strong acid and weak base are acidic, and salts of a strong base and weak acid are alkaline.