Question

Define the term neutralisation :

(a) Give a reaction, mentioning clearly acid and base used in the reaction

(b) If one mole of a strong acid reacts with one mole of a strong base, the heat produced is always the same. Why?

Answer 1

1. When an acid reacts with a base to form salt and water, it is called a neutralisation reaction.
$Acid+Alkali⟶Salt+Water$.

(a) Two examples are

2. The reaction between hydrochloric acid and sodium hydroxide

$HCl+NaOH⟶NaCl+H_{2}O$

3. The reaction between sodium carbonate and sulphuric acid.

$N{a}_{2}C{O}_3+H_{2}S{O}_4⟶N{a}_{2}C{O}_3+H_{2}O+C{O}_2$

(b)
Two points will help you understand I think.

1. a strong acid or base completely dissociates in water to form ions.
2. The ionic equation for any strong acid and a strong base is:

$HA+BOH⟶H_{2}O\left(l\right)+AB$

$H^{+}+A^{-}+B^{+}+O{H}^{-}⟶H_{2}O\left(l\right)+A^{-}+B^{+}$

Because $A^{-}$ and $B^{+}$ appear on both sides, they cancel out and you are left with

$H^{+}+O{H}^{-}⟶H_{2}O\left(l\right)$

This is always the net ionic equation for a reaction of this type, so the enthalpy of that reaction will determine the heat produced.

Note: I used a hydroxide as my strong base because it makes it simpler. Not all strong bases are hydroxides, but they all form hydroxide in water, so you get the same result.

A specific example:

$HCl+NaOH⟶H_{2}O\left(l\right)+NaCl$

the ionic equation is:

$H^{+}+C{l}^{-}+N{a}^{+}+O{H}^{-}⟶H_{2}O\left(l\right)+N{a}^{+}+C{l}^{-}$

$N{a}^{+}$ and $C{l}^{-}$ cancel out, so you are left with :

$H^{+}+O{H}^{-}⟶H_{2}O\left(l\right)$