Exploring Changes in Matter

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

• Burning wood

• Melting ice

• Rusting iron

• Baking a cake

Answer explanation

Melting ice is a physical change because it involves a change in state from solid to liquid without altering the chemical composition. In contrast, burning wood, rusting iron, and baking a cake involve chemical changes.

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NGSS.MS-PS1-4

What is the Law of Conservation of Mass?

• Mass is created during a chemical reaction.

• Mass is destroyed during a chemical reaction.

• Mass is conserved and remains constant during physical and chemical changes.

• Mass can be converted into energy.

Answer explanation

The Law of Conservation of Mass states that mass is conserved and remains constant during physical and chemical changes, meaning it is neither created nor destroyed in these processes.

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NGSS.MS-PS1-2

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Which of the following best describes a chemical change?

• A change in the state of matter

• A change in color, temperature, or the formation of a gas

• A change in size or shape

• A change in texture

Answer explanation

A chemical change involves a transformation that alters the substance's chemical composition, often indicated by changes in color, temperature, or the formation of gas, making this choice the best description.

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NGSS.MS-PS1-2

If 10 grams of hydrogen react with 80 grams of oxygen to form water, what is the total mass of water produced?

• 70 grams

• 80 grams

• 90 grams

• 100 grams

Answer explanation

According to the law of conservation of mass, the total mass of reactants equals the total mass of products. Here, 10g of hydrogen + 80g of oxygen = 90g of water produced.

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NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which of the following processes is a chemical change?

• Dissolving sugar in water

• Freezing water

• Cooking an egg

• Cutting paper

Answer explanation

Cooking an egg is a chemical change because it alters the proteins in the egg, resulting in a new substance. In contrast, dissolving sugar, freezing water, and cutting paper are physical changes.

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NGSS.MS-PS1-2

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How does increasing temperature generally affect the rate of a chemical reaction?

• It decreases the rate of reaction.

• It has no effect on the rate of reaction.

• It increases the rate of reaction.

• It stops the reaction completely.

Answer explanation

Increasing temperature generally increases the rate of a chemical reaction. This is because higher temperatures provide more energy to the reactant molecules, leading to more frequent and effective collisions.

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NGSS.HS-PS1-5

Explain why mass is conserved in a chemical reaction using the Law of Conservation of Mass.

• Mass is conserved because atoms are rearranged but not created or destroyed.

• Mass is conserved because energy is converted into mass.

• Mass is conserved because new atoms are created.

• Mass is conserved because atoms are destroyed.

Answer explanation

Mass is conserved in a chemical reaction because the Law of Conservation of Mass states that atoms are rearranged but not created or destroyed, ensuring the total mass remains constant.

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NGSS.MS-PS1-5

Which of the following is a sign that a chemical change has occurred?

• A substance changes from solid to liquid.

• A substance changes color.

• A substance changes shape.

• A substance changes size.

Answer explanation

A change in color indicates a chemical change, as it often signifies the formation of new substances. In contrast, changes in state, shape, or size are typically physical changes.

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NGSS.MS-PS1-2

A student heats a mixture of baking soda and vinegar. What evidence would support that a chemical change has occurred?

• The mixture cools down.

• The mixture changes color.

• Bubbles form, indicating gas production.

• The mixture becomes a solid.

Answer explanation

Bubbles forming indicate gas production, a clear sign of a chemical change. This occurs when baking soda reacts with vinegar, producing carbon dioxide gas, which is evidence of a new substance being formed.

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NGSS.MS-PS1-2

Describe how temperature affects the rate of a chemical reaction using an example.

• Increasing temperature decreases the rate of rusting.

• Increasing temperature increases the rate of ice melting.

• Increasing temperature increases the rate of sugar dissolving.

• Increasing temperature increases the rate of food cooking.

Answer explanation

Increasing temperature increases the kinetic energy of molecules, leading to more frequent and effective collisions. This is evident in cooking, where higher temperatures speed up the cooking process by enhancing reaction rates.

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