Which of the following equations represents a reaction that provides the heat of formation of NaClO3? Solution The standard enthalpy of formation is the change in enthalpy for one mole of a substance in the standard state formed from its pure elements under the same conditions. here the pure elements are Na (s), Cl2 (g) and O2 (g ) Na(s) + Cl(g) + 1/2 O2(g) ? NaClO3(s) used pure elements but reaction is not balanced. so not desired rection so the answer is Na(s) + 1/2 Cl2(g) + 3/2 O2(g) ? NaClO3(s) where all the elements are in its standard state and reaction is balanced for 1 mole of product .

1. Which of the following equations represents a reaction that provides the heat of formation of
NaClO3?
NaClO2(s) + O(g) ? NaClO3(s)
Solution
The standard enthalpy of formation is the change in enthalpy for one mole of a substance in the
standard state formed from its pure elements under the same conditions.
here the pure elements are Na (s), Cl2 (g) and O2 (g )
Na(s) + Cl(g) + 1/2 O2(g) ? NaClO3(s) used pure elements but reaction is not balanced. so not
desired rection
so the answer is
Na(s) + 1/2 Cl2(g) + 3/2 O2(g) ? NaClO3(s)
where all the elements are in its standard state and reaction is balanced for 1 mole of product