Topic 2: Chemical Changes

How is a solid different from a liquid?

• A solid can flow and take the shape of its container, while a liquid has a fixed shape.

• A solid has a variable shape and volume, while a liquid has a definite shape and volume.

• A solid is always less dense than a liquid, making it float on top.

• A solid has a definite shape and volume, while a liquid has a definite volume but takes the shape of its container.

Answer explanation

A solid has a definite shape and volume, meaning it retains its form. In contrast, a liquid has a definite volume but adapts to the shape of its container, making the correct choice clear.

Tags

NGSS.MS-PS3-4

How are a solid and a liquid different from a gas?

• Solids have fixed shapes and volumes, liquids have fixed volumes and gases do not have either fixed shapes or volumes.

• Liquids expand to fill their container, while solids do not change shape.

• Solids can flow like liquids, but gases cannot.

• Gases have fixed shapes and volumes, while solids and liquids do not.

Answer explanation

Solids and liquids maintain fixed shapes and volumes, unlike gases, which expand to fill their containers. This distinction is key in understanding the properties of different states of matter.

Tags

NGSS.MS-PS1-4

Which process is an example of a chemical change?

• Bread is toasted

• Oil soaks through a shirt

• A girl forms a soap bubble

• Red food coloring spreads out in water

Answer explanation

Toasting bread is a chemical change because it alters the bread's composition, creating new flavors and textures through the Maillard reaction. The other options involve physical changes, not chemical transformations.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

What happens to the particles of substances when a chemical change occurs?

• The particles rearrange to form new substances with different properties.

• The particles remain unchanged and retain their original properties.

• The particles disappear completely during the change.

• The particles only change their color without forming new substances.

Answer explanation

When a chemical change occurs, the particles rearrange to form new substances with different properties, distinguishing it from physical changes where the particles remain unchanged.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which statement describes something that occurs only during a physical change?

• a new substance forms

• chemical properties change

• the substances gain or lose mass

• the properties of substances stay the same

Answer explanation

During a physical change, the properties of substances stay the same, meaning their chemical identity is unchanged. In contrast, a new substance forms or chemical properties change during a chemical change.

Tags

NGSS.MS-PS1-4

Which statement describes what happens when sugar dissolves in water?

• Sugar particles attach to the water particles.

• A new substance with new properties forms.

• The sugar particles change into a different kind of particle.

• The particles of both substances become evenly spread apart.

Answer explanation

When sugar dissolves in water, the sugar particles disperse among the water particles, leading to an even distribution. This means the correct statement is that the particles of both substances become evenly spread apart.

Tags

NGSS.MS-PS1-2

How do you know that a chemical change has occurred?

• Signs of a chemical change include color change, gas production, precipitate formation, temperature change, and odor change.

• The substance changes state from solid to liquid.

• The mass of the substance increases significantly.

• The substance becomes more transparent.

Answer explanation

A chemical change is indicated by signs such as color change, gas production, precipitate formation, temperature change, and odor change. These signs confirm that a new substance has formed, unlike physical changes.

Tags

NGSS.MS-PS1-2

The scientist added 0.5 grams of a solid to 2 grams of a liquid. Can you predict the total weight of the substances after the materials were mixed?

• 0.5 grams

• 3 grams

• 2.5 grams

• 1.5 grams

Answer explanation

To find the total weight after mixing, add the weight of the solid (0.5 grams) to the weight of the liquid (2 grams). Thus, 0.5 + 2 = 2.5 grams, making the correct answer 2.5 grams.

Tags

NGSS.MS-PS1-5

A young scientist found 2 liters of an unlabeled solution of white liquid in a glass jar. She wanted to find out what some of the properties of the substance were. So, she tested the substance.

Which conclusion can you draw about what has happened to the solution when it was mixed with an acid?

• the solution was separated by a physical change only

• the solution was broken down into its smallest particles

• the solution was changed chemically into new substances

• the solution was changed physically

Answer explanation

When the solution was mixed with an acid, it underwent a chemical change, resulting in the formation of new substances. This indicates a reaction occurred, distinguishing it from mere physical changes.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

The scientist noticed a gas rising from the solution while boiling it. Afterwards, she noticed that there was less mass remaining than when she started. How can this phenomenon be explained?

• boiling destroyed some of the matter in the solution

• boiling resulted in a chemical change that altered the solution's properties

• boiling resulted in a state change from a liquid to a gas

• boiling caused the solution to clump together, increasing the total density of the solution

Answer explanation

The gas rising from the solution indicates that boiling caused a state change from liquid to gas. This process results in a loss of mass as the gas escapes into the air, explaining the decrease in mass observed.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4