What is the location on an enzyme that chemical reactions happen on?
The active site
The area that the substrate binds to is called the active site of the enzyme. The active site is VERY specific- only one substrate will fit into it. Also remember that the enzyme can be reused after each reaction (lots of people tend to forget that so that's just a little tip to not forget)
A good little way to remember this is by thinking of a lock and key. The substrate is the key, and the active site of the enzyme is the lock. Only that specific "key" will fit into the lock.You cant stick your car key into the lock on your front door and expect it to work, and the same is true for enzymes.