Catalysts

Which statement correctly describes a chemical reaction?

Bonds between atoms break and reform.

Which statement best describes the amount of catalyst that remains at the end of a reaction?

The amount of catalyst is the same at the end as at the beginning of the reaction.

Which statement best describes how a catalyst can speed up a chemical reaction?

The catalyst decreases the reaction energy needed.

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.

Photosynthesis is an example of

an endothermic reaction

How does a catalyst work?

by decreasing the activation energy of a reaction

Which term describes an enzyme?

catalyst

Lactase and carbonic anhydrase are examples of what type of substance?

enzyme

The lock-and-key mechanism refers to

the complementary shapes of an enzyme and a substrate.

Which is the best definition of activation energy?

the energy required to form or break the bonds of reactant molecules