Does any iron fuse in stars before they go supernova?
I understand that iron and all heavier elements consume more energy to produce than they make, and that is what eventually leads to a supernova. I also understand that a lot of the heavier elements are produced during that supernova. However, what I'm wondering is, before the star goes supernova, does any of the iron fuse with other elements? Yes, there would be a net energy loss, but if there is only small amount of iron in the star, it would probably be able to handle that.
Yes, but it's slow. (I'm not an expert, so feel free to correct if I miss something important), but once the star is into the later stages, past the helium stage, up to iron, fusion mostly takes place by fusing a helium onto a heavier element, raising each atomic number by 2. That's not the only method but it's the most common.
Iron can also fuse into nickel in this way inside a star and it does in small amounts, but mostly beyond iron, and certainly beyond nickel, heavier elements are created through the S-Process. (short for slow neutron capture process). This happens when a free neutron binds to the atomic nucleus and over time, the addition of neutrons can lead to beta decay, where an electron is ejected and a proton remains - adding to the atomic number.
but if there is only small amount of iron in the star, it would
probably be able to handle that.
This is undoubtedly true. The stars that go super-nova are incredibly large and the iron doesn't exactly sink to the core right away. It takes some time. For a star to go kablooie (supernova), it needs an iron core of both enough purity where it's no longer undergoing expansion from nearby fusion, and enough size for it to undergo rapid collapse in a way that effects the star around it almost instantaneously. I'm not clear on the exact process, but it requires way more than just a little iron. As a layman's guess, it might require a Jupiter sized ball of iron. Perhaps a fair bit more than that.