Chemical Reactions Quiz

What are the 5 signs that a chemical reaction has occurred?

1. Color Change 2. Production of an odor 3. Change of Temperature (heat or light) 4. Evolution of a gas (formation of bubbles) 5. Precipitate (formation of a solid from a solution)

How do physical and chemical changes differ on a molecular level?

A physical change, such as a state change or dissolving, does not create a new substance, but a chemical change does. In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

Where do the elements come from that make up the products of a chemical reaction?

In a chemical reaction, only the atoms present in the reactants can end up in the products. No new atoms are created, and no atoms are destroyed.

If the Law of Conservation of Mass states that "no new matter is created and no matter is destroyed", then how come in a chemical reaction new products are formed?

No new elements are created in a chemical reaction, however new products are formed from the elements in the reactants. In a chemical reaction, only the atoms present in the reactants can end up in the products. No new atoms are created , and no atoms are destroyed.

Why, on a molecular level, does changing the amount of reactants affect the amount of products created?

Products are made from the reactants, so adding more reactants will produce more products.

What is the name of the arrow sign? What does the arrow represent in a chemical equation?

The arrow is called the 'yields' sign. It means "equals"

What is the Law of Conservation of Mass?

The same amount and types of atoms are found in the reactants and the products. Matter is neither created nor destroyed in a chemical reaction.

What name is given to the large '2' before the sodium bicarbonate and sodium chloride molecules? What does this number tell you?

This is called a coefficient. It tells you that how many of a particular molecule there are. In this equation, the 2 before the sodium bicarbonate molecules says that there are 2 molecules of sodium bicarbonate (and the same for sodium chloride).

What is the name given to the small '3' after the oxygen atoms in sodium bicarbonate and calcium carbonate? What does this number tell you?

This is called a subscript. It tells you how many of a certain type of atom are in the molecule. In this equation, the 3 after the oxygen atom in the sodium bicarbonate molecule tells you there are 3 atoms of oxygen in every molecule of sodium bicarbonate.

What is a chemical change? (chemical reaction)

are usually irreversible changes involving the rearrangement of the atoms of one or more substances and a change in their chemical composition, resulting in the formation of at least one new substance. The substance cannot be changed back to its original form - it becomes a different substance.

CaCO3

calcium, carbon, oxygen - calcium carbonate (chalk)

CO2

carbon, oxygen; carbon dioxide

HCl

hydrogen, chlorine; hydrochloric acid

H2O

hydrogen, oxygen; water

FeO2

iron, oxygen - iron oxide (rust)

What is a physical change?

is any change that does NOT involve a change in the substance's chemical identity. Physical changes are those changes that do not result in the production of a new substance.

NaCl

sodium, chlorine; sodium chloride (salt)