Question

in a chemical reaction, the atoms of the reactants are rearranged to form products with different chemical and physical properties. a catalyst is a substance that speeds the rate at which a chemical reaction takes place. the catalyst itself is unchanged at the end of the reaction. in which of the following reactions is a catalyst at work? 1. when an acid is neutralized, as when hydrochloric acid is added to sodium hydroxide yielding sodium chloride and water 2. when food is digested, as when an enzyme in saliva called ptyalin breaks down starch into sugars without itself changing 3. when copper is oxidized by combining with nitric acid to yield copper nitrate, nitrogen dioxide and water 4. when baking soda is heated, causing the sodium bicarbonate to break down, yielding carbon dioxide gas as a by - product

Explanation:

A catalyst is a substance that speeds up a chemical reaction without being consumed in the reaction. In the given examples, the enzyme ptyalin in saliva is a catalyst as it breaks down starch into sugars without itself changing.

Answer:

When food is digested, as when an enzyme in saliva called ptyalin breaks down starch into sugars without itself changing.