States of Matter and Phase Changes Review

The Law of Conservation of Energy states that energy cannot be created or destroyed, but energy can change

• its total mass

• its total volume

• from one form to another

• from one state of matter to another

Answer explanation

The Law of Conservation of Energy states that energy can change from one form to another, such as from kinetic to potential energy, but it cannot be created or destroyed. Thus, the correct choice is 'from one form to another'.

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The normal melting and freezing points for water are

• 0°C—melting temperature, and 100°C—freezing temperature

• 100°C—melting temperature, and 0°C—freezing temperature

• 0°C for both

• 100°C for both

Answer explanation

The normal melting point of water is 0°C, where it changes from solid (ice) to liquid (water). The freezing point is also 0°C, where water turns back into ice. Thus, the correct answer is 0°C for both.

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NGSS.MS-PS1-4

An increase in the motion of molecules occurs when

• heat energy changes randomly.

• heat energy is stable.

• heat energy is added.

• heat energy is removed.

Answer explanation

An increase in the motion of molecules occurs when heat energy is added. This added energy causes molecules to move faster, increasing their kinetic energy and overall motion.

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Heat flows between two objects that are close to each other if the objects have different

• specific heats

• temperatures

• masses

• densities

Answer explanation

Heat flows between two objects when there is a temperature difference. The object with a higher temperature transfers heat to the one with a lower temperature, making 'temperatures' the correct choice.

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Which two processes increase the motion of the molecules?

• A and B

• B and C

• C and D

• D and A

Answer explanation

Processes C and D typically involve heating or agitation, which increase the energy and motion of molecules. This is why they are the correct choices for increasing molecular motion.

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Which process is represented by B?

• condensing

• evaporating

• freezing

• melting

Answer explanation

The process represented by B is evaporating, which occurs when a liquid turns into vapor. This is the opposite of condensing, where vapor turns back into liquid. The other options, freezing and melting, refer to solid and liquid states.

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Some students were building models of solids, liquids, and gases by gluing plastic balls to a sheet of cardboard. Which of their models best shows the particles in a solid?

• Option 1

• Option 2

• Option 3

• Option 4

Answer explanation

Option 4 best represents particles in a solid, as it shows them closely packed in a fixed arrangement, reflecting the strong intermolecular forces and limited movement characteristic of solids.

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Base your answer to the following question on the diagram below and on your knowledge of science. The diagram shows a sequence of events. The ball and ring are made of the same metal. State the relationship between the temperature of the metal ball and the speed of the molecules moving in the ball.

Answer explanation

As the temperature of the metal ball increases, the speed of the molecules moving in the ball also increases. This is because higher temperatures provide more energy to the molecules, causing them to move faster.

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The diagram below represents liquid water in a pan on a hot plate. The liquid water is boiling and changing into water vapor. The process of boiling is considered to be a

• chemical change, because a new substance is formed

• chemical change, because a new substance is not formed

• physical change, because a new substance is formed

• physical change, because a new substance is not formed

Answer explanation

Boiling water is a physical change because it involves a change in state from liquid to gas without forming a new substance. The water vapor is still water, just in a different form.

Which process occurs when dry ice, solid carbon dioxide, is changed directly into gaseous carbon dioxide?

• crystallization

• condensation

• sublimation

• solidification

Answer explanation

The process of dry ice changing directly from solid to gas is called sublimation. This occurs without passing through the liquid phase, making sublimation the correct answer.

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