Science Unit 2, Lesson 20

A sample of liquid water is heated on a hot stove. What property of the water changes aong with the increase in temperature?

• As the temperature increases, the water molecules gain oxygen and lose hydrogen.

• When the temperature reaches the boiling point, the water changes state.

• When the temperature reaches the boiling point, the water changes into another substance.

• As the temperature increases, the water molecules become larger and move more slowly.

A sample of ice is placed on a warm kitchen counter. What property of the ice changes along with the increase in temperature?

• When the temperature reaches the melting point, the ice changes state.

• As the temperature increases, the water molecules gain oxygen and lose hydrogen.

• When the temperature reaches the melting point, the ice changes into another substance.

• As the temperature increases, the water molecules become larger and move more slowly.

A sample of liquid water is placed in a freezer. What property of the water changes along with the decrease in temperature?

• As the temperature decreases, the water molecules gain oxygen and lose hydrogen.

• When the temperature reaches the freezing point, the water changes into another substance.

• When the temperature reaches the freezing point, the water changes states.

• As the temperature decreases, the water molecules become smaller and move more rapidly.

When a tablet is dropped into water, the tablet releases tiny bubbles that make a fizzing noise. Gradually the tablet disappears into the water, which becomes cloudy.

Did substances in the tablet enter a chemical reaction with the water?

• Yes. Dissolving in water is a common sign of a chemical change.

• No. Dissolving in water is an example of a physical change, not a chemical change.

• No. The water becoming cloudy is an example of a physical change, not a chemical change.

• Yes. A change in state without heating or cooling is a common sign of a chemical change.

When drops of one liquid are added to another liquid, a purple powder forms where the liquids meet.

Did the two liquids enter a chemical reaction?

• Yes. The mixing of two liquids is a common sign of a chemical reaction.

• Yes. A change in state without heating or cooling is a common sign of a chemical reaction.

• No. Substances entering or leaving a solution are examples of physical changes, not chemical changes.

• No. A chemical reaction usually forms gases, not solids.

When methane gas is heated in the presence of air, a blue flame appears. The flame is hot!

Does the blue flame show that a chemical reaction is occurring?

• No. Burning a fuel involves physical changes, not chemical changes.

• Yes. A change in color always indicates a chemical reaction is occurring.

• Yes. The release of energy is a common sign of a chemical reaction.

• No. A chemical change always involves a change of state.

The law states that the amount of matter stays the same during (a)   changes to matter. If 200 kilograms of matter enter a process that changes, then the outcome must have a mass equal to 200 kilograms.​

• any chemical or physical
• conservation
• dissolving

Over many years, an acorn grows into a tall, massive oak tree.

Does the law of conservation of mass apply to this example?

• No. The law of conservation of mass only applies to chemicals, not plants or animals.

• Yes. The mass of a growing plant comes from materials in its environment.

• No. Plants perform photosynthesis, a process that involves sunlight.

• Yes. The mass of a growing plant comes from sunlight.

During the course of a few weeks, a tiny dandelion seed may grow into an adult plant.

Does the law of conservation of mass apply to this example?

• No. The law of conservation of mass only applies to chemicals, not plants and animals.

• Yes. The mass of a growing plant comes from sunlight.

• Yes. The mass of a growing plant comes from materials in its environment.

• No. Plants perform photosynthesis, a process that involves sunlight.

Over many years, a log on the forest floor will gradually decompose and rot away.

Does the law of conservation of mass apply to this example?

• Yes. The matter of the log is changed into simpler materials, including gases in the air.

• No. The law of conservation of mass only applies to chemicals, not plants and animals.

• Yes. The matter of the log is changed into energy.

• No. Decomposers include fungi, which live by breaking apart dead materials for their energy.