Chemical Change

Chemical Change

Multiple Choice

Liz is exploring the different kinds of changes that can happen to substances. She knows that changes can alter the looks or shape of a substance. Cutting, melting, bending, or crushing are examples of what kind of change?

• reactant

• product

• physical

• chemical

Multiple Choice

Liz is exploring the different kinds of changes that can happen to substances.  After reading about the kinds of changes that occur, she saw some rust on a pipe that was going into her house. What kind of change is the formation of rust?

• reactant

• product

• physical

• chemical

Multiple Select

After learning about chemical reactions, Olivia investigated different kinds of chemical changes using substances she found in her kitchen so she could see these changes. Which of the following can occur when a chemical reaction takes place? Choose the three statements that apply.

• New bonds form.

• Existing bonds break.

• New substances form.

• Changes don't affect matter.

​Example of a Chemical Reaction

​The bonds of the reactants break. The atoms rearrange and new bonds are formed when the products are formed.

Multiple Choice

Kim understands that there are several signs that indicate a chemical reaction has occurred. What is the best way to be certain that a chemical reaction has occurred?

• Some bubbles form.

• A color change occurs.

• A new substance forms.

• The materials do not react.

​Explanation

​The correct answer is “A new substance forms,” which indicates a chemical reaction has taken place. A color change may signal a chemical change, but it does not confirm definitely that one has taken place. Formation of bubbles can be an observable change from a chemical reaction, but it does not necessarily mean a chemical change occurred. For example, bubbles can form if the pressure of a liquid decreases. The materials in a chemical change do react, so that answer is incorrect.

Multiple Select

Some chemical reactions need energy in the form of heat to take place, while others give off energy. Read each of the phrases that describe reactions where energy is released or absorbed. Which phrases suggest that energy has been absorbed?  Check all that apply.

• need continuous source of energy

• energy available is greater then the energy needed to break bonds

• leaves surroundings feeling cold

• more energy needed to break bonds of the reactants than is available

Multiple Select

Some chemical reactions need energy in the form of heat to take place, while others give off energy. Read each of the phrases that describe reactions where energy is released or absorbed. Which phrases suggest that energy has been released?  Check all that apply.

• light is produced

• heat is produced

• more energy needed to break bonds of the reactants than is available

• need continuous source of energy

​Explanation

​The correct answers are: reaction where energy is absorbed, which needs a continuous source of energy, leaves the surroundings feeling cold, and more energy is needed to break bonds of the reactants than is available. On the other hand, in a reaction where energy is released, light can be produced, the energy available is greater than the energy needed to break bonds, and heat may be produced.