<p>The standard heat of formation of sodium ions in aqueous solution from the following data will be:</p>

<p>Heat of solution NaOH(aq.) from NaOH(s) = -470.7 kJ</p>

<p>Heat of formation of&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>O</mi><msup><mi>H</mi><mo>-</mo></msup></math>(aq.) from&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>O</mi><msup><mi>H</mi><mo>-</mo></msup><mo>(</mo><mi>s</mi><mo>)</mo></math>&nbsp;= -228.8 kJ</p>