Why strong acid neutralize will give out more energy than weak acid neutralize?
- 老爺子Lv 71 十年前最愛解答
Strong acids and strong alkalis are completely dissociated in water to give H^+(aq) ions and OH^-(aq) respectively, while weak acids and weak alkalis are partially dissociated.
Suppose a strong alkali is used in both titrations.
In titration between a strong acid and a strong alkali, the actual reaction is between H^+(aq) and OH^-(aq) ions. Therefore, no matter what strong acid or strong alkali are used, the enthalpy change of neutralization is constant.
In titration between a weak acid and a strong alkali, the actual reaction is also between H^+(aq) and OH^-(aq) ions, but H^+(aq) ions are formed from the partial dissociation (partial ionization) of the weak acid. When H^+(aq) ions are reacted, the equilibrium position of the ionization of the weak acid is shift to produce more H^+(aq) ions. At the equivalence point, the weak acid is completely ionized to give H^+(aq) ions, which is then completely neutralized by the OH^-(aq) ions from the strong alkali. Since SOME ENERGY RELEASED IN NEUTRALIZATION IS CONSUMED TO IONIZE THE WEAK ACID, less energy is released to the surroundings.
2007-03-20 11:54:20 補充：
若果如第一位回答者所言，形成少左水。即係用少左 H^ (aq) 或者 OH^ (aq)，咁中和都未完成，所以這答案是不正確的。
- ?Lv 51 十年前
By observing the molecules of H2O formed, we can derive the result of energy released
i.e. The more H2O molecules is released, the more energy is released (in the form of
heat) as neutralization is an exothermic reaction.
Strong acid is completely ionized when dissolved in water, which more H+ ions would
be released. But weak acid could only partly ionized to form H+ ions.
In that case, there are more H+ mobile ions in a certain molarity and volume of strong
acid than the weak one. The more H+ ions is released, the more chances for the H+
ions to react with the OH- ions.
As the result, more resulting salt is formed ( more reactions between H+ and OH- ions)
when strong acid neutralizes with an alkaline.
Therefore more energy in the form of heat is released.
2007-03-19 23:31:09 補充：