Characteristics of Chemical Reactions

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

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

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

• Hydrogen molecules are negative, and oxygen is positive.

• Oxygen atoms are much larger than hydrogen atoms.

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

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

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

• A new substance with different properties is formed.

• The substance seems to disappear after dissolving in water.

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

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Which observations ate evidence that a chemical reaction took place?

• Observation 1

• Observation 2

• Observation 3

• Observation 4

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When vinegar and baking soda are combined, bubbles begin to form. Explain how the formation of bubbles is evidence of a chemical reaction.

• Form a new product

• Regroup into a new molecule

• Makes new atoms

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Four students performed four different investigations by combining different substances. Their results are shown in the table below. In which experiment did a chemical reaction take place, and how do you know?

• Experiment 1: bubbles are produced and that is evidence that a chemical reaction took place.

• Experiment 2: water level rises and that is evidence that a chemical reaction took place.

• Experiment 3: Crystal's dissolve completely and that is evidence that a chemical reaction took place.

• Experiment 4: solid sinks to the bottom of the container and that is evidence that a chemical reaction took place.

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

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

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

• We know combining Substance 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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The smallest particle of elements; made of electrons, protons, and metrons.

• Atom

• Molecules

• Precipitate

• Reactant

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The smallest particle of elements; made of electrons, protons, and metrons.

• Atom

• Molecules

• Precipitate

• Reactant

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