Lesson 8: Chemical Changes Quiz 2

Which of the following is a chemical change?

• Melting ice

• Burning wood

• Cutting paper

Answer explanation

Burning wood is a chemical change because it transforms the wood into ash and gases through combustion, altering its chemical structure. In contrast, melting ice and cutting paper are physical changes.

During a chemical change, what happens to the atoms?

• Rearrange to form new substances

• Disappear

• Move farther apart but stay the same substance

Answer explanation

During a chemical change, atoms rearrange to form new substances, which is why the correct answer is 'Rearrange to form new substances'. They do not disappear or simply move apart while remaining the same.

What factor most directly changes particle motion and interactions?

• Temperature

• Color

• Container shape

Answer explanation

Temperature directly affects the kinetic energy of particles, influencing their motion and interactions. Higher temperatures increase particle speed and collisions, while lower temperatures slow them down.

In a physical change, the substance:

• Becomes a new substance

• Stays the same substance

• Always warms up

Answer explanation

In a physical change, the substance undergoes changes in form or appearance but retains its original chemical identity. Therefore, it stays the same substance, making this the correct choice.

Which is a physical change?

• Baking a cake

• Rusting iron

• Dissolving sugar in water

Answer explanation

Dissolving sugar in water is a physical change because it involves a change in state without altering the chemical composition of the sugar. In contrast, baking a cake and rusting iron involve chemical changes.

When water freezes, what changes?

• Identity changes to a new substance

• Atoms rearrange into new molecules

Answer explanation

When water freezes, it changes from liquid to solid state, but its chemical identity remains the same as H₂O. Thus, only the state changes, confirming the correct choice.

Which sign best supports a chemical change?

• Bubbles from boiling water on a hot plate

• A new solid forms when two clear liquids are mixed

• Ice melts in a warm room

Answer explanation

A new solid forming when two clear liquids are mixed indicates a chemical change, as it shows a reaction has occurred, resulting in a substance with different properties. The other options describe physical changes.

Which is NOT good evidence of a chemical change by itself?

• Temperature change from an external heater

• Light produced during a reaction

• Gas produced at room temperature

Answer explanation

A temperature change from an external heater does not indicate a chemical change by itself, as it may result from physical processes. In contrast, light produced and gas released are strong indicators of chemical reactions.

Mixing baking soda and vinegar causes fizzing because:

• It is a physical change

• A gas forms in a chemical reaction

• The vinegar boils

Answer explanation

Mixing baking soda and vinegar produces carbon dioxide gas, which causes fizzing. This is a result of a chemical reaction, making 'A gas forms in a chemical reaction' the correct choice.

Freezing, grinding, and evaporating are examples of:

• Physical changes

• Chemical changes

Answer explanation

Freezing, grinding, and evaporating are all processes that change the state or appearance of a substance without altering its chemical composition, making them examples of physical changes.