Characteristics of Chemical Reactions CFA

Hydrogen and oxygen react to form water. At an atomic level, how do we know that a chemical reaction has occurred?

• Hydrogen molecules are negative, and oxygen positive.

• For every oxygen atom, two hydrogen atoms are needed.

• The hydrogen and oxygen atoms regroup into a new molecule.

• Oxygen atoms are much larger than hydrogen atoms.

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OK.7.PS1.2

The chart below shows the results of combining various substances. Which of the following statements is true?

• We know combining Substances A and B resulted in a chemical reaction because a gas was formed.

• We know combining Substances C and D resulted in a chemical reaction because of the lack of a temperature change.

• We know combining Substances A and B resulted in a chemical reaction because of the lack of a temperature change.

• We know that neither combinations resulted in a chemical reaction because neither one had a color change.

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OK.7.PS1.2

Which of the following is the best description of the results of a chemical reaction?

• A new substance with different properties is formed.

• The substance seems to disappear after dissolving in water.

• The substance changes from liquid to solid at a low temperature.

• The reaction can be reversed to get back the original substance.

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OK.7.PS1.2

Rust forming on a piece of iron is an example of which of the following:

• A physical change because the process can be reversed

• The natural process of decay as metallic ions age

• A chemical change because oxygen atoms from the atmosphere bonded with the iron atoms

• A violation of the laws of physics because new mass has been created

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OK.7.PS1.2

Which of the following statements is true?

• Cutting paper is an example of a chemical reaction because a new substance is formed and the process cannot be undone.

• Freezing water is an example of a chemical reaction because a new substance is formed and the process cannot be undone.

• Burning paper is an example of a chemical reaction because a new substance is formed and the process cannot be undone.

• Melting ice is an example of a chemical reaction because a new substance is formed and the process cannot be undone.

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OK.7.PS1.2