Unit 7 - Chemical Reactions And Energy

1. Which of the following is a chemical reaction?

Rust forming on a car body

Water evaporating from salt water leaving salt crystals

Water freezing into ice

Dew forming on grass

Rust forming on a car body is a chemical reaction because it involves a chemical change. Rust is formed when iron reacts with oxygen in the presence of moisture, resulting in the formation of iron oxide. This process is known as oxidation and is a chemical reaction.

Explanation

Rust forming on a car body is a chemical reaction because it involves a chemical change. Rust is formed when iron reacts with oxygen in the presence of moisture, resulting in the formation of iron oxide. This process is known as oxidation and is a chemical reaction.

2. When iron combines with oxygen and water in the air to form rust, what substance in the reaction is the product?

Rust

Iron

Oxygen

Water

When iron combines with oxygen and water in the air, it undergoes a chemical reaction to form rust. Rust is the product of this reaction, which means it is the substance that is produced as a result of the reaction.

Explanation

When iron combines with oxygen and water in the air, it undergoes a chemical reaction to form rust. Rust is the product of this reaction, which means it is the substance that is produced as a result of the reaction.

3. A(n) ______ is a substance that speeds up a chemical reaction without being permanently changed itself.

Catalyst

Inhibitor

Exotherm

Endotherm

A catalyst is a substance that speeds up a chemical reaction without being permanently changed itself. It works by lowering the activation energy required for the reaction to occur, allowing the reaction to proceed at a faster rate. Catalysts can be used in various industries such as the production of chemicals, pharmaceuticals, and energy. They are essential in increasing the efficiency and reducing the cost of many chemical processes.

Explanation

A catalyst is a substance that speeds up a chemical reaction without being permanently changed itself. It works by lowering the activation energy required for the reaction to occur, allowing the reaction to proceed at a faster rate. Catalysts can be used in various industries such as the production of chemicals, pharmaceuticals, and energy. They are essential in increasing the efficiency and reducing the cost of many chemical processes.

4. Which of the following symbols in a chemical equation means "produces"?

+

[p]

(aq)

The symbol "+" in a chemical equation means "produces".

Explanation

The symbol "+" in a chemical equation means "produces".

5. As a result of the experiment of Lavoisier, you know that in a chemical reaction the mass of the products ______.

Is twice as great as the mass of the reactants

Is less than the mass of the reactants

Always equals the mass of the reactants

Cannot be predicted based on the mass of the reactants

In the experiment conducted by Lavoisier, it was observed that the mass of the products formed in a chemical reaction is always equal to the mass of the reactants. This observation is known as the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. Therefore, the correct answer is that the mass of the products always equals the mass of the reactants.

Explanation

In the experiment conducted by Lavoisier, it was observed that the mass of the products formed in a chemical reaction is always equal to the mass of the reactants. This observation is known as the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. Therefore, the correct answer is that the mass of the products always equals the mass of the reactants.