Question

Does combustion have a negative entropy or positive entropy?

Answer 1

It really depends, but most likely a positive entropy.

If the number of gas molecules increases during a process, the change in entropy will be positive. In the combustion of propane:

`C_3H_8 (g) + 5O_2(g) -> 3CO_2(g) + 4H_2O(g)`

there are 6 molecules of gas on the left, and 7 molecules of gas on the right. The increase in gas molecules increases the disorder, and therefore the change in entropy is positive.

Very clear explanation on this page: http://www.chemistry-reference.com/rxns/