Question

A student designs an experiment to test substances X, Y, and Z, to determine which one is a catalyst for the reaction: A + B ® C. Only one of the unknown substances is a catalyst, and the others are nonreactive with A, B, or C. When 10 mL of A is added to 10 mL of B, the reaction takes twenty seconds. Bubbles form when the product C is created. The student prepares three test tubes, each containing both reactants A and B. She adds unknowns X, Y, and Z to test tubes 1, 2, and 3, respectively. She then times the reaction in each test tube from the point when the unknown is added until bubbling stops. How can the student identify the catalyst? The test tube that stops bubbling first contains the catalyst. The test tube that produces the most bubbles contains the catalyst. The test tube that bubbles the longest contains the catalyst. The test tube that does not bubble contains the catalyst.

Answer 1

The test tube with the catalyst will be the test tube that stops bubbling first.
Catalysts act by reducing the activation energy of a given reaction, which means that the reaction is able to proceed more easily. This reduction in activation energy is achieved by providing the reaction an alternate pathway to follow.
When the reaction is carried out more easily, it also occurs more rapidly and finishes in less time. Therefore, the bubbling will stop earlier than without a catalyst.