Unit 7 Chemical Reactions

The number of atoms you begin with in a chemical reaction ...

• must be the same as the number of  atoms you end with

• must be an even number

• can be different to the number you finish with

• changes depending on how much energy is formed

Answer explanation

In a chemical reaction, the law of conservation of mass states that the number of atoms must remain constant. Therefore, the number of atoms you begin with must be the same as the number of atoms you end with.

Tags

NGSS.MS-PS1-5

Balance the following:

____ Fe + ____ Cl₂ → ____ FeCl₃

• 1,1,2

• 1,3,1

• 2,2,3

• 2,3,2

Answer explanation

To balance the equation, we need 2 Fe and 3 Cl atoms to produce 2 FeCl3. Thus, the balanced equation is 2 Fe + 3 Cl2 → 2 FeCl3, making the correct coefficients 2, 3, 2.

Tags

NGSS.MS-PS1-5

Balancing the following:

____ Al + ____ HCl → ____ AlCl₃ + ____ H₂

• 1,3,1,2

• 2,3,2,3

• 2,6,2,3

• 3,2,6,2

Answer explanation

To balance the equation, we need 2 Al, 6 HCl, producing 2 AlCl3 and 3 H2. This ensures the number of each type of atom is equal on both sides, confirming the correct coefficients are 2, 6, 2, 3.

Tags

NGSS.MS-PS1-5

Which type of reaction is:

2 NaBr + Ca(OH)₂ → CaBr₂ + 2 NaOH

• Synthesis

• Single Displacement

• Double Displacement

• Combustion

Answer explanation

This reaction involves the exchange of ions between two compounds, NaBr and Ca(OH)2, resulting in the formation of CaBr2 and NaOH. This characteristic of exchanging partners defines it as a Double Displacement reaction.

Tags

NGSS.MS-PS1-2

Which type of reaction is: C₂H₄ + 3 O₂ → 2 CO₂ + 2 H₂O

• Synthesis

• Decomposition

• Single Displacement

• Combustion

Answer explanation

The reaction C2H4 + 3 O2 → 2 CO2 + 2 H2O involves the combustion of ethylene (C2H4) in the presence of oxygen (O2), producing carbon dioxide (CO2) and water (H2O), which classifies it as a combustion reaction.

Tags

NGSS.MS-PS1-2

Which type of reaction is:

2 H₃AsO₄ → As₂O₅ + 3 H₂O

• Synthesis

• Decomposition

• Single Displacement

• Combustion

Answer explanation

The reaction 2 H₃AsO₄ → As₂O₅ + 3 H₂O involves the breakdown of a single compound (H₃AsO₄) into simpler products (As₂O₅ and H₂O), which characterizes it as a decomposition reaction.

Tags

NGSS.MS-PS1-2

Which type of reaction is:

2 NH₃ + H₂SO₄ → (NH₄)₂SO₄

• Synthesis

• Decomposition

• Single Displacement

• Double Displacement

Answer explanation

The reaction 2 NH3 + H2SO4 → (NH4)2SO4 involves the combination of ammonia and sulfuric acid to form ammonium sulfate. This is a synthesis reaction, where simpler substances combine to form a more complex product.

Tags

NGSS.MS-PS1-2

Which type of reaction is:

3 Pb + 2 H₃PO₄ → 3 H₂ + Pb₃(PO₄)₂

• Synthesis

• Single Displacement

• Double Displacement

• Combustion

Answer explanation

This reaction involves lead (Pb) displacing hydrogen (H) from phosphoric acid (H3PO4), forming hydrogen gas (H2) and lead(II) phosphate (Pb3(PO4)2). This characteristic of one element replacing another defines it as a Single Displacement reaction.

Which type of reaction is:

C₇H₁₆ + 10 O₂ → 7 CO₂ + 8 H₂O

• Synthesis

• Decomposition

• Single Displacement

• Combustion

Answer explanation

The reaction C7H16 + 10 O2 → 7 CO2 + 8 H2O is a combustion reaction, where a hydrocarbon (C7H16) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O), releasing energy.

Tags

NGSS.MS-PS1-2

Which type of reaction is:

4 (NH₄)₃PO₄ + 3 Pb(NO₃)₄ → 12 NH₄NO₃ + Pb₃(PO₄)₄

• Synthesis

• Decomposition

• Single Displacement

• Double Displacement

Answer explanation

This reaction involves the exchange of ions between two compounds, (NH4)3PO4 and Pb(NO3)4, resulting in the formation of NH4NO3 and Pb3(PO4)4. This characteristic makes it a double displacement reaction.

Tags

NGSS.MS-PS1-2