Answer
$\Delta H = -6.237 kJ $
Work Step by Step
2 KClO3 --> 2 KCl + 3O2 $\Delta H = -89.4 kJ $
From the coefficients we see that for the production of 2 moles of KCl, that 89.4 kJ of heat are released. To find how much is released for 10.4 g of KCl, we need to convert this to moles so we must find the molecular mass of KCl:
K has a mass of 39.083 g/mol
Cl has a mass of 35.45 g/mol
KCl has a mass of 74.533 g/mol
Then we have 10.4 g * (1mol KCl/ 74.533 g) * (-89.4 kJ/ 2 mole KCl) = -6.237 kJ
