Onion Chemistry: Chemical Changes Exam

What type of change occurs when an onion is chopped, releasing a pungent odor and causing tears?

• Physical change

• Chemical change

• State change

• Phase separation

What enzyme is responsible for initiating the tear-inducing reaction in onions?

• Catalase

• Amylase

• Alliinase

• Lactase

What compound is directly responsible for making your eyes water when an onion is chopped?

• Sulfur dioxide

• syn-Propanethial-S-oxide

• Hydrogen sulfide

• Acetic acid

Cooking an onion causes which of the following processes?

• Hydrolysis

• Thermal decomposition

• Neutralization

• Freezing

Which type of evidence would best support that a chemical change occurred during cooking?

• The onion became cold

• The onion softened

• The onion released new smells and turned brown

• The onion was sliced thinly

What happens to the enzyme alliinase when onions are cooked at high heat?

• It speeds up

• It becomes stronger

• It denatures and stops working

• It multiplies

Which of the following best describes thermal decomposition?

• The release of water from boiling

• The rearrangement of atoms without energy change

• A chemical breakdown caused by heat

• A physical breakdown of shape

Which of these is NOT evidence of a chemical change in onions?

• Production of a new odor

• Browning of the onion

• Tears from syn-Propanethial-S-oxide

• Cutting the onion into pieces

What type of bond is broken during a chemical change in cooking onions?

• Ionic bond

• Covalent bond

• Intermolecular force

• Hydrogen bond

Which term best describes a reaction that absorbs heat from its surroundings?

• Exothermic

• Endothermic

• Combustion

• Catalytic