Chemical Formula and Reaction

Ethane (C₂H₆) is one of many compounds that burns in oxygen to form carbon dioxide and water. What is true of the chemical equation shown below?

C₂H₆+ O₂ --> CO₂ + H₂O

• The positions of the reactants and the products are reversed.

• The formulas of the reactants and the products are not correct.

• The equation is not balanced, so it does not show conservation of mass.

• The types of atoms present on the reactant side are not the same as those on the product side.

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One way in which a nuclear reaction is different from a chemical reaction is that the identity of the atom itself might change as a result of the reaction. Which of the following will cause an atom to change into an atom of a different element?

• The atom gains or loses energy.

• The atom gains or loses protons.

• The atom gains or loses neutrons.

• The atom gains or loses electrons

The image above represents energy changes that occur during a chemical reaction. Based on the image, what can you infer?

• A. The reaction is exothermic.

• B. The reaction is endothermic.

• C. The reaction destroys energy.

• D. The reaction creates energy.

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Why does decreasing the temperature of a reaction decrease the rate at which the reaction occurs?

• A. Lower temperatures decrease the amount of catalyst present.

• B. Lower temperatures decrease the number of reactant particles.

• C. Lower temperatures cause particles to move more slowly and collide less often.

• D. Lower temperatures decrease the sizes of the reactant particles so they collide less often.

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NGSS.HS-PS1-5

The following appears in a chemical equation: 3C₂H₄ How many atoms of carbon are represented by this formula?

• 2

• 3

• 5

• 6

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The following chemical equations represent three different chemical reactions.

3NaOH + H₃PO₄ --> Na₃PO₄ + 3H₂O

2Mg + O₂ --> 2MgO

Pb(NO₃)₂ + 2NaI --> PbI₂ +2NaNO₃

Based on these equations, which statement is true?

• A. Mass is lost when 2Mg and O₂ become 2MgO.

• B. Because Mg and O₂ are both elements, no bonds were broken during the formation of MgO.

• C. The chemical properties of Pb(NO₃)₂ and NaI differ from the chemical properties of PbI₂ and NaNO₃.

• D. The chemical properties of NaOH and Na₃PO₄ are similar, and the chemical properties of H₃PO₄ and H₂O are similar.

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What property of carbon is the primary reason it can form so many different types of compounds?

• A. A carbon atom contains six protons in its nucleus.

• B. Each carbon atom contains four valence electrons.

• C. Certain carbon isotopes are capable of radioactive decay.

• D. Carbon exists in nature in solid, liquid, and gaseous states.

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What is the cause of the large amount of energy produced in a nuclear fission reaction?

• A. The nucleus of a large atom splits into two smaller nuclei that have less mass than the large atom.

• B. The nucleus of a large atom absorbs electrons from smaller atoms.

• C. Nuclei of smaller atoms form bonds that bring them closer together.

• D. Nuclei of smaller atoms combine to form a new, more massive nucleus.

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NGSS.HS-PS1-8

The diagram shows the structural formula for hexane. Based on the diagram, which of the following is the chemical formula for hexane?

• A. C₃H₆

• B. C₄H₈

• C. C₆H₆

• D. C₆H₁₄

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NGSS.MS-PS1-1

Which of the following statements accurately describes the kinds of elements that can undergo radioactive decay?

• A. All elements undergo radioactive decay.

• B. Elements with unstable nuclei undergo decay.

• C. Only elements created in laboratories undergo decay.

• D. Elements with more neutrons than protons undergo decay

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