Identifying Chemical Reactions

Which of the following is a common sign of a chemical reaction?

• Change in temperature

• Melting of ice

• Dissolving sugar in water

• Breaking a glass

Answer explanation

A common sign of a chemical reaction is a change in temperature, indicating that energy is being absorbed or released. Melting ice, dissolving sugar, and breaking glass are physical changes, not chemical reactions.

Tags

NGSS.MS-PS1-2

A solid forms when two substances are mixed. Which indicator of a chemical reaction is this?

• Formation of a precipitate

• Production of Light

• Change in odor

• Change in Temperature

Answer explanation

The formation of a solid when two substances are mixed indicates a chemical reaction known as a precipitate. This is a key indicator of a chemical change, distinguishing it from other indicators like light or temperature changes.

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NGSS.MS-PS1-2

Which of the following is NOT a sign of a chemical reaction?

• Production of gas

• Change in color

• Boiling of water

• Emission of light

Answer explanation

Boiling of water is a physical change, not a chemical reaction. The other options—production of gas, change in color, and emission of light—are indicative of chemical reactions occurring.

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NGSS.MS-PS1-2

What does the formation of bubbles in a liquid usually indicate?

• A physical change

• A chemical reaction

• A change in state

• A change in pressure

Answer explanation

The formation of bubbles in a liquid typically indicates a chemical reaction, as gases are often produced during such reactions. This is distinct from physical changes or changes in state, which do not necessarily produce gas bubbles.

Tags

NGSS.MS-PS1-2

Which of the following is an example of a chemical change?

• Rusting of iron

• Melting of butter

• Boiling of water

• Breaking a stick

Answer explanation

Rusting of iron is a chemical change because it involves a reaction with oxygen, forming iron oxide. In contrast, melting butter, boiling water, and breaking a stick are physical changes, as they do not alter the substance's chemical composition.

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NGSS.MS-PS1-2

NGSS.MS-PS1-5

What is a common indicator of a chemical change?

• Absorption of heat

• Change in shape

• Change in size

• Change in texture

Answer explanation

A common indicator of a chemical change is the absorption of heat, which often signifies a reaction occurring. Changes in shape, size, or texture may occur in physical changes, not necessarily indicating a chemical change.

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NGSS.MS-PS1-2

NGSS.MS-PS1-4

Which of the following observations suggests a chemical reaction has occurred?

• A solid dissolves in water

• A liquid turns into a gas

• A new odor is produced

• A liquid freezes

Answer explanation

A new odor is produced indicates a chemical reaction, as it often results from the formation of new substances. The other options may involve physical changes, not necessarily indicating a chemical reaction.

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NGSS.MS-PS1-2

Which of the following is a sign of a chemical reaction involving light?

• A light bulb turning on

• A glow stick glowing

• A candle melting

• A mirror reflecting light

Answer explanation

A glow stick glowing is a clear sign of a chemical reaction involving light, known as chemiluminescence. In contrast, a light bulb turning on involves electrical energy, a candle melting is a physical change, and a mirror reflects light.

What is an indicator of a chemical change when a substance burns?

• Change in mass

• Change in color

• Production of heat and light

• Change in volume

Answer explanation

The production of heat and light is a clear indicator of a chemical change during burning, as it signifies a reaction occurring. Other options may not consistently indicate a chemical change.

Tags

NGSS.MS-PS1-2

Which statement best describe a chemical change?

• A chemical change only involves a change in physical appearance.

• A chemical change results in the formation of new substances.

• A chemical change can be reversed easily without any new substances formed.

• A chemical change involves changing a property of substance without changing its identity

Answer explanation

A chemical change results in the formation of new substances, distinguishing it from physical changes, which only alter appearance. The correct choice highlights this key aspect of chemical reactions.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5