# Question #a1bda

Feb 27, 2017

Here's what's going on here.

#### Explanation:

The enthalpy change of reaction when a strong acid is neutralized by a strong base is actually

$\Delta {H}_{\text{rxn" = -"57 kJ mol}}^{- 1}$

which means that $\text{57 kJ}$ of heat are being given off, hence the minus sign, when $1$ mole of strong acid is being neutralized by $1$ mole of strong base.

In your case, nitric acid, a strong acid, and potassium hydroxide, a strong base, will neutralize each other in a $1 : 1$ mole ratio as shown by the balanced chemical equation

${\text{HNO"_ (3(aq)) + "KOH"_ ((aq)) -> "H"_ 2"O"_ ((l)) + "KNO}}_{3 \left(a q\right)}$

Notice that if you have $0.5$ moles of nitric acid and only $0.2$ moles of potassium hydroxide, the strong base will act as a limiting reagent, i.e. it will be completely consumed before all the moles of nitric acid get the chance to take part in the react.

Therefore, this reaction will consume $0.2$ moles of potassium hydroxide and $0.2$ moles of nitric acid -- think $1 : 1$ mole ratio here!

You can thus say that this reaction will give off

$0.2 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{moles HNO"_3))) * "57 kJ given off"/(1color(red)(cancel(color(black)("mole HNO"_3)))) = color(darkgreen)(ul(color(black)("11.4 kJ given off}}}}$

I'll leave the answer rounded to three sig figs, but keep in mind that your values do not justify three significant figures for the answer.