EL#04 Chemical Reactions Review

The law of conservation of mass states that:

• Mass can be created or destroyed in a chemical reaction.

• Mass is neither created nor destroyed in a chemical reaction.

• Mass is always increased in a chemical reaction.

• Mass is always decreased in a chemical reaction.

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NGSS.MS-PS1-5

Is this balanced? 2Al + N₂ → 2AlN

• Balanced

• Unbalanced

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Is this balanced? KI + Cl₂ → 2KCl + I₂

• Balanced

• Unbalanced

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Count the atoms for each element: C₈H₁₀N₄O₂.

• Carbon = 8, Hydrogen = 10, Nitrogen = 4, Oxygen = 2

• Carbon = 6, Hydrogen = 12, Nitrogen = 2, Oxygen = 1

• Carbon = 7, Hydrogen = 8, Nitrogen = 3, Oxygen = 2

• Carbon = 8, Hydrogen = 9, Nitrogen = 4, Oxygen = 3

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NGSS.MS-PS1-1

9. Which of the following best defines a 'chemical change'?

• A change in which the substance retains its original properties.

• A change that only affects the physical appearance of a substance.

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

• A change that can be easily reversed by physical means.

Why is frying an egg considered a chemical reaction?

• Because it changes the physical state of the egg.

• Because it involves a change in the chemical composition of the egg.

• Because it is a reversible process.

• Because it only involves heat transfer.

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12. What are the signs or evidence a chemical reaction has occurred?

• Change in color, temperature, formation of a precipitate, or gas production

• Increase in mass and volume

• Decrease in temperature and pressure

• No observable change

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NGSS.MS-PS1-2

13. How do we know for certain a chemical reaction has occurred? THINK ATOMS!

• Change in color

• Formation of a precipitate

• Emission of gas

• Rearrangement of atoms

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Define “compound”.

• A substance formed when two or more chemical elements are chemically bonded together.

• A single element in its pure form.

• A mixture of different substances that are not chemically bonded.

• A type of chemical reaction.

Label the following as a molecule or atom. O₂: _______, O: _______, H₂O: _______, C: _______, H: _______, N₂: _______.

• O₂: molecule, O: atom, H₂O: molecule, C: atom, H: atom, N₂: molecule.

• O₂: atom, O: molecule, H₂O: atom, C: molecule, H: molecule, N₂: atom.

• O₂: molecule, O: molecule, H₂O: atom, C: atom, H: molecule, N₂: molecule.

• O₂: atom, O: atom, H₂O: molecule, C: molecule, H: atom, N₂: atom.

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NGSS.MS-PS1-1