Why would zinc powder burn more vigorously in oxygen that zinc foil?

The previous answer is correct but lacks some detail.





A Zinc foil has bonds between the zinc molecules. One way to think about it is this: Zinc foil has two sides that can touch oxygen. If you were to separate all the zinc molecules, or at least make it into a powder, you'd now have many more sides for the oxygen to come in contact with the zinc and therefore burns more vigorously.





In the case of foil, the oxygen contacts with only the exposed molecules first, has to interact with them and 'burn', once that interaction has taken place then another oxygen molecule has to come in contact with the next layer, and so on.





So, if you were to take zinc foil and grind it down into a powder, you are effectively increasing the surface area where the oxygen molecules can interact with zinc, meaning more interactions can happen at the same time.Why would zinc powder burn more vigorously in oxygen that zinc foil?
This is a common way of increasing the rate of reaction.Rate of reaction is proportional to the available sites for diferrent reagents.By using the powder rather than foil you let the oxygen to be in contact with more sites of zinc so what you say , happens.Why would zinc powder burn more vigorously in oxygen that zinc foil?
Greater surface area in the powder, more collisions per second, more productive collisions per second, faster rate of reaction.