Manganese metal can be obtained by the reaction of manganese dioxide with aluminium. 4al(s)+3mno2(s) 2 al2o3(s)+3 mn(s) calculate the enthalpy change of reaction. given: 2al(s)+3/2 o2(8) ao3(s) ah-1680 kj mol mn(s)+o2(g) mno2(s) -520 kj mol1. ah

Explanation:

We have the following reaction:

And we are given thermodinamic data from the two following reactions:

According to Hess's Law, if we can somehow combine both ecuations to get the first one, we can sum both to get the total change of enthalpy.

We identify that in the second ecuation, is on the right side, and we want it to be on the left side. We can invert that ecuation and that means getting the opposite :

Now, before combining both ecuations, we must get the same stoichometric coefficents present on the one we want to obtain. For that, just multiply the first one by 2 and the second one by 3, that means also multipying the corresponding :

Now, just sum both ecuations to get the original one: