Reviewing Chemical Reactions

Front

Which of the following is a sign that a chemical reaction has occurred?

• The substance changes shape
• A gas is produced
• The substance is cut into pieces
• The temperature remains the same

Back

A gas is produced

Answer explanation

A gas is produced is a clear sign of a chemical reaction, indicating new substances are formed. The other options do not necessarily indicate a chemical change, as they can occur without a reaction.

Tags

NY.SCI.6-8.MS-PS1-2

Front

What does the Law of Conservation of Mass state about atoms during a chemical reaction?

Back

The total number of atoms stays the same

Answer explanation

The Law of Conservation of Mass states that during a chemical reaction, the total number of atoms remains constant. This means atoms are neither created nor destroyed, ensuring the total count stays the same.

Tags

NY.SCI.6-8.MS-PS1-5

Front

Which device is designed to absorb thermal energy during a physical process? Options: A hand warmer, An ice pack, A light bulb, A toaster

Back

An ice pack

Answer explanation

An ice pack is designed to absorb thermal energy, making it effective for reducing swelling and pain by drawing heat away from the body. In contrast, a hand warmer, light bulb, and toaster generate heat rather than absorb it.

Tags

NY.SCI.6-8.MS-PS1-6

Front

Which of the following is NOT a property that can be used to identify a substance before and after a chemical reaction? Color, Mass, Shape, Reactivity

Back

Shape

Answer explanation

Shape is not a reliable property for identifying a substance before and after a chemical reaction, as it can change without a chemical change. In contrast, color, mass, and reactivity are consistent identifiers.

Tags

NY.SCI.6-8.MS-PS1-2

Front

Back

2

Answer explanation

In the reaction 2H2 + O2 → 2H2O, there are 2 oxygen atoms on the left side (from O2) and 2 oxygen atoms on the right side (in 2H2O). Thus, the correct answer is 2.

Tags

NY.SCI.6-8.MS-PS1-5

Front

Which of the following is an example of a device that releases thermal energy during a chemical reaction? A cold pack, A hand warmer, A refrigerator, An ice cube tray

Back

A hand warmer

Answer explanation

A hand warmer releases thermal energy through an exothermic chemical reaction, providing heat. In contrast, a cold pack absorbs heat, a refrigerator removes heat, and an ice cube tray does not involve a chemical reaction.

Tags

NY.SCI.6-8.MS-PS1-6

Front

Which observation best indicates that a chemical reaction has taken place?

Back

A new substance with different properties forms

Answer explanation

A new substance with different properties forms is the best indicator of a chemical reaction. This signifies that the original substances have undergone a transformation, resulting in new characteristics.

Tags

NY.SCI.6-8.MS-PS1-2

Front

If you start with 10 grams of reactants in a closed system, how much mass of products should you expect after the reaction?

Back

10 grams

Answer explanation

According to the law of conservation of mass, the total mass of reactants equals the total mass of products in a closed system. Therefore, starting with 10 grams of reactants, you should expect 10 grams of products.

Tags

NY.SCI.6-8.MS-PS1-5

Front

Which device is designed to release thermal energy during a physical process? Options: An ice pack, A hand warmer, A fan, A thermometer

Back

A hand warmer

Answer explanation

A hand warmer is specifically designed to release thermal energy through exothermic chemical reactions, providing warmth. In contrast, an ice pack cools, a fan circulates air, and a thermometer measures temperature without releasing heat.

Tags

NY.SCI.6-8.MS-PS1-6

Front

Which observations indicate a chemical reaction between two substances?

Back

Change in color, formation of a gas, and temperature change

Answer explanation

The best indicators of a chemical reaction are observable changes such as a change in color, formation of a gas, and temperature change. These signs suggest that new substances may have formed.

Tags

NY.SCI.6-8.MS-PS1-2