Unit 2 Chemical Reactions

In this equation, how many atoms are in the nitrogen (N2) molecule?

• 2

• 6

• 3

• 1

This chemical formula represents caffeine.

4C₈H₁₀N₄O₂

How many molecules of caffeine are present?

• 2

• 4

• 96

• 32

True or False:

Chemical Formulas are used to identify substances, and

The elements and the number of atoms of each element present in a chemical formula are used to identify substances.

• True

• False

The formula below represents common household cleaning ingredient known as vinegar. It is commonly mixed with baking soda to clean.

CH₃COOH

Which information can be determined from the chemical formula?

• The structure of the molecule.

• The color of vinegar.

• The size of vinegar.

• The number of atoms of each element in vinegar.

Which formulas have the same number of oxygen atoms?

• Carbon dioxide and Magnesium Oxide

• Sodium Chloride and Copper Sulphate

• Copper Sulphate and Magnesium Oxide

• Copper Sulfate and Sulphuric Acid

A student placed 5 grams of yeast into a beaker, and 30 mL of hydrogen peroxide into a flask. The student then poured the hydrogen peroxide into the beaker with yeast. The student immediately observed foaming bubbles in the flask.

An accurate conclusion would be that -

• a physical change was occuring

• the yeast and hydrogen peroxide were products

• the gas was oxygen

• the bubbles indicated that this was a chemical change.

This chemical equation demonstrates that...

• the reactants are the same substances as the products

• the number of molecules in the reactants is equal to the number of molecules in the products

• the atoms are changed into different atoms

• matter cannot be created or destroyed

What is formed during a chemical reaction?

• Mass

• Products

• Atoms

• Reactants

A scientist performed an investigation in which different solid substances were added to four different beakers containing the same amount of water. After stirring the combined substances for two minutes, the scientists recorded the observations in the table below.

The results of which of the above investigations indicates that the substances least likely reacted chemically?

• 1

• 2

• 3

• 4

Which reaction best supports the law of conservation of mass?

• 2H₂O₂ → H₂O + O₂

• H₂O₂ → 2H₂O + O₂

• 2H₂O₂ → 2H₂O + O₂

• 2H₂O₂ → 2H₂O + 2O₂