Question

How many grams of KClO3 must be decomposed to obtain 48.7 J of heat?

2KClO3(s) ---> 2KCl(s) + 3O2(g)
∆H° = –78.0 kJ

Answer 1

The delta-H in thermo equations acts just like a stoichiometric coefficient, so 2mol KClO3 will release 78kJ of energy. Since you only need to release 48.7kJ, your conversion is:
\[48.7kJ * (2mol KClO{_3})/(78kJ) = 1.25mol KClO{_3}\]
Now that you have moles of KClO3, use the molar mass of KClO3 (122.5g/mol) to convert to grams. You should get about 153g of KClO3

Answer 2

thanks!