Chemistry Semester 2 Final exam 2023-203-24

A teacher asks her students to examine titles of four scientific articles. Which titled article is specifically about a chemical change?

• How Baking Soda Reacts with Vinegar

• How Rust Can Be Scraped off of Metal

• How Metals Respond to Electrical Currents

• How Elements Can Change Phase When Heated

Identify ALL of the chemical changes

• Boiling water

• Burning a marshmallow

• Fireworks going off

• Cutting your hair

• Dying your hair

If you cut a wooden block in half, each half would have:

• Half the density of the original piece

• Twice the density of the original piece

• The same density as the original piece

Which best represents a balanced equation?

• 120 grams of carbon plus 20 grams of oxygen → 200 grams of carbon dioxide

• 120 grams of carbon plus 50 grams of oxygen → 200 grams of carbon dioxide

• 120 grams of carbon plus 80 grams of oxygen → 200 grams of carbon dioxide

The following chemical reaction occurs.

2H2O2 → 2H2O + O2

How many atoms of hydrogen are involved in the reaction?

• 1

• 2

• 4

• 8

The compound ammonia is composed of nitrogen and hydrogen atoms. If two atoms of nitrogen completely react with six atoms of hydrogen to form two molecules of ammonia, which best describes the number of hydrogen atoms present in the two molecules of ammonia?

• 2

• 4

• 6

Which is best represented by the equation?

2Mg + O₂ 2MgO

• Law of Conservation of Energy

• Law of Conservation of Mass

• Law of Superposition

When chemicals react in a closed container, which must be true?

• The mass both before and after the reaction is the same.

• The mass both before and after the reaction is variable.

• The same number of compounds is present both before and after the reaction.

A chemistry teacher combines 20 grams of lemon juice with 25 grams of baking soda in a flask covered with a balloon. The flask and balloon have a combined mass of 105 grams. What is the mass of the entire setup after a reaction has occurred?

• 45 g

• 150 g

• 605 g

The equation below shows a reaction between sodium (Na) and water (H2O).

2Na (s) + H2O (l) → 2NaOH (aq) + H2 (g)

Which best explains why the equation is not balanced?

• There is too much sodium in the reactants.

• There is not enough water in the reactants.

• There is too much hydrogen gas in the products.

• There is not enough sodium hydroxide in the products.