Question 3
What do iron rusting, fruit ripening, firewood burning and a firecracker going off all have in common?
The right answer is the one marked above.
They are all chemical reactions. In every one of them reactants are used up and new products with different properties are formed.
They certainly do not all happen at the same speed — that is the whole point of this chapter. Neither reversibility nor a catalyst is required for a chemical reaction.