Jesse M. answered • 04/28/23
AP Chemistry Tutor at a Learning Center
I have an analogy that may help. Imagine trying to fit into a tight sweatshirt. You may have to contort your body and strain your neck getting it on, but eventually it'll sit comfortably on your body. In this case, you and the sweatshirt represent the starting material, and the now fully dressed you is the product. In the case of a chemical reaction, in order to form products, the starting material must line up perfectly, with the correct orientation, and with enough energy to overcome an unnatural, strained position.
A catalyst is useful because it provides support (for lack of a bette word) and allows the starting material to comfortably arrange itself so that it no longer has to be positioned in such a particular and strained position. Back to the sweatshirt example; you can imagine having a couple friends stretching out the sweatshirt a little so you just slide right into it. Note that the process itself changed, but the starting materials and product are identical. Catalysts work similarly.
Because of this, we say that the catalyst alters the mechanism of the reaction. So answer choice A is correct.
B. Catalysts do not effect the change in H
C. Same as B
D. Catalysts DO change the Ea of a reaction. They lower it which allows the reaction to proceed faster. However, catalysts also lower the Ea of the reverse reaction, so D is wrong.
I hope this helped. Please feel free to reach out if you have anymore questions/need to clarify anything :)
