A solid 30.2 cm^3 block of KClO₃ is heated and decomposes according to the following reaction. What is the change in enthalpy in kj when all the KClO₃ decomposes? The density of KClO₃ is 2.34 g/cm^3

Question

2KClO₃(s) → 2KCl(s) + 3O₂(g) ∆H = -89.4 kj

I tried a few different conversions but none of them gave me the right answer

Answer 1

So, since we know the density of KClO3, and the volume of the KClO3 block, we can calculate the mass of the block:

30.2 cm3 x 2.34 g/cm3 = 70.668 g KClO3

Now, we convert this to moles of KClO3:

70.668 g KClO3 x 1 mol/122.6 g = 0.5764 moles KClO3

From the balanced equation we see that decomposition of TWO moles KClO3 generates 89.4 kJ of heat.

Thus, we can now find kJ of heat generated by 0.5764 moles KClO3:

0.5764 moles x 89.4 kJ/2 moles = 25.8 kJ (the sign would be negative since heat is released)