Unit 6 Review: Chemical Reactions

Which equation illustrates conservation of mass?

• H₂ + Cl₂ → 2 HCl

• H₂ + Cl₂ → HCl

• H₂ + O₂ → H₂O

• H₂ + O₂ → 2 H₂O

Answer explanation

The equation H₂ + Cl₂ → 2 HCl illustrates conservation of mass as it shows that the number of atoms of each element is the same on both sides of the equation, confirming that mass is conserved during the reaction.

Tags

NGSS.MS-PS1-5

Which equation shows a conservation of mass?

• Na + Cl₂ → NaCl

• H₂O → H₂ + O₂

• PCl₅ → PCl₃ + Cl₂

• Al + Br₂ → AlBr₃

Answer explanation

The equation Al + Br₂ → AlBr₃ shows conservation of mass as the number of atoms of each element is the same on both sides: 1 Al and 2 Br atoms react to form 1 AlBr₃, maintaining the total mass.

Tags

NGSS.MS-PS1-5

In which type of chemical reaction do two or more reactants combine to form one product, only?

• single replacement

• double replacement

• decomposition

• synthesis

Answer explanation

In a synthesis reaction, two or more reactants combine to form a single product. This distinguishes it from other types like single replacement, double replacement, and decomposition, which involve different processes.

Given the balanced equation representing a reaction: Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g) Which type of reaction is represented by this equation?

• synthesis

• single replacement

• decomposition

• double replacement

Answer explanation

This reaction involves zinc displacing hydrogen from sulfuric acid, forming zinc sulfate and hydrogen gas. This is characteristic of a single replacement reaction, where one element replaces another in a compound.

Which equation represents a decomposition reaction?

• CaCO₃(s) → CaO(s) + CO₂(g)

• KOH(aq) + HCl(aq) → KCl(aq) + H₂O(l)

• Cu(s) + 2AgNO₃(aq) → 2Ag(s) + Cu(NO₃)₂(aq)

• 2H₂(g) + O₂(g) → 2H₂O(l)

Answer explanation

The equation CaCO₃(s) → CaO(s) + CO₂(g) represents a decomposition reaction, where a single compound (calcium carbonate) breaks down into two products (calcium oxide and carbon dioxide).

Which Lewis electron-dot diagram is correct for a S²⁻ ion?

• A

• B

• C

• D

Answer explanation

The correct Lewis electron-dot diagram for a S²⁻ ion is [:S:]²⁻, which shows sulfur with 8 valence electrons (6 from sulfur and 2 additional from the negative charge). The other options do not accurately represent the electron configuration.

Tags

NGSS.HS-PS1-2

What is the net charge of an ion that has 8 protons, 9 neutrons, and 10 electrons?

• 1+

• 2+

• 1-

• 2-

Answer explanation

An ion's net charge is calculated by subtracting the number of electrons from the number of protons. Here, 8 protons - 10 electrons = -2, resulting in a net charge of 2-. Thus, the correct answer is 2-.

The total number of electrons in a neutral atom of every element is always equal to the atom's

• number of neutrons

• number of atomic particles

• mass number

• number of protons

Answer explanation

In a neutral atom, the number of electrons equals the number of protons to balance the charge. Therefore, the total number of electrons in a neutral atom is always equal to the atom's number of protons.

This equation represents the formation of a

• fluorine atom by losing an electron

• fluoride ion by gaining an electron

• fluorine atom by gaining an electron

• fluoride ion by losing an electron

Answer explanation

The equation F + e⁻ → [F]⁻ shows fluorine (F) gaining an electron (e⁻) to form a negatively charged ion, known as a fluoride ion ([F]⁻). Thus, the correct choice is 'fluoride ion by gaining an electron'.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

When an F atom becomes an F⁻ ion, the F atom

• loses a proton

• loses an electron

• gains an electron

• gains a proton

Answer explanation

When an F atom becomes an F⁻ ion, it gains an electron. This addition of an electron gives the ion a negative charge, distinguishing it from the neutral atom.