Which of the reactions below are catalyzed? check all that apply. amylase in saliva increases the rate at which starch in food breaks down. the amylase to break down the starch, but it is not consumed during the reaction. magnesium metal reacts with hydrochloric acid to produce hydrogen gas and magnesium chloride. the reaction rate increases if the magnesium is crushed to a powder before adding the hydrochloric acid. ethene gas can react with hydrogen to form ethane gas, a component of natural gas. the rate of the reaction increases if powdered nickel or palladium are present. formic acid can decompose to form carbon monoxide and water. in the presence of another acid, this reaction proceeds more quickly because the second acid forms an intermediate, highly reactive complex that can then break down, releasing the acid for further reaction.

Answers are:

1) Amylase in saliva increases the rate at which starch in food breaks down. The amylase helps to break down the starch, but it is not consumed during the reaction.

2) Ethene gas can react with hydrogen to form ethane gas, a component of natural gas. The rate of the reaction increases if powdered nickel or palladium are present.

3) Formic acid can decompose to form carbon monoxide and water. In the presence of another acid, this reaction proceeds more quickly because the second acid forms an intermediate, highly reactive complex that can then break down, releasing the acid for further reaction.

A catalyst is a chemical species that is present at the beginning of a reaction and reappears at the end.  

An intermediate forms during the reaction and disappears before the end.

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst.  

Reactions occur faster with a catalyst because they require less activation energy.

the answers are 1,3, and 4