Neutralisation Between “Strong Acid and Strong Alkali” vs “Weak Acid and Strong Alkali”


  1. Table below shows comparison of the heat of neutralisation of the reaction between "strong acid and strong alkali" and "weak acid and strong alkali".

Strong Acid and Strong Alkali
Weak Acid and Strong Alkali
HCl + NaOH → NaCl + H2O
∆H = -57kJ mol-1
CH3COOH + NaOH → CH3COONa +H2O
∆H = -55kJ mol-1
H2SO4 + 2KOH → K2SO4 + 2H2O
∆H = -57kJ mol-1
HCN + KOH → KCN + H2O
∆H = -12kJ mol-1
2HNO3 + Ba(OH)2 → Ba(NO3)2 + 2H2O
∆H = -57kJ mol-1

  1. The heat of neutralisation between strong acid and strong alkali is almost the same (-57kJ mol-1 ) for all acid and all alkali.
  2. Nevertheless, the heat of neutralisation between weak acid and strong alkali is always less than -57kJ mol-1.
  3. This is because weak acids are partially decomposed.
  4. During the reaction of neutralisation, the acid molecules will be decomposed to form hydrogen ions and react with the hydroxide ions from alkali.
  5. Part of the heat released during the formation of water molecule is used to decompose the acid to form hydrogen ion.


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